WEBVTT 1 00:00:00.520 --> 00:00:06.080 Section seventeen of the Science History of the Universe, Volume four. 2 00:00:07.000 --> 00:00:10.599 This is a LibriVox recording. All LibriVox recordings are in 3 00:00:10.640 --> 00:00:14.160 the public domain. For more information or to volunteer, please 4 00:00:14.240 --> 00:00:20.879 visit LibriVox dot org. Recording by Avay in June twenty seventeen, 5 00:00:22.199 --> 00:00:26.879 The Science History of the Universe, Volume four, edited by 6 00:00:26.920 --> 00:00:34.880 Francis Rold Wheeler. Chemistry, Chapter thirteen, valence the constitution of 7 00:00:35.079 --> 00:00:43.520 organic compounds and the development of stereochemistry. In the preceding chapter. 8 00:00:43.759 --> 00:00:47.240 Mention has been made of the influence exerted by Frankland 9 00:00:47.320 --> 00:00:51.479 on the views developed by Colbert respecting the constitution of 10 00:00:51.719 --> 00:00:56.719 organic compounds. It was Frankland who, in his now classical 11 00:00:56.759 --> 00:01:02.679 paper A New Series of Organic Compounds containing metals, demonstrated 12 00:01:02.920 --> 00:01:05.959 that the peering of the radicals with the elements was 13 00:01:06.000 --> 00:01:09.400 to be explained on the ground of some characteristic property 14 00:01:09.480 --> 00:01:12.959 of the atoms, and thus he expelled the useless part 15 00:01:13.079 --> 00:01:19.200 of the radical theory. Eighteen fifty two. Frankland observed that 16 00:01:21.200 --> 00:01:26.280 when the formulae of inorganic chemical compounds are considered, even 17 00:01:26.319 --> 00:01:29.680 a superficial observer is struck with the general symmetry of 18 00:01:29.719 --> 00:01:35.519 their constitution. The compounds of nitrogen, phosphorus, antimony, and arsenic 19 00:01:35.680 --> 00:01:40.359 especially exhibit the tendency of these elements to form compounds 20 00:01:40.359 --> 00:01:44.760 containing three or five equivalents of other elements, and it 21 00:01:44.840 --> 00:01:49.480 is in these proportions that their affinities are best satisfied. Thus, 22 00:01:49.560 --> 00:01:53.680 an eternal group, we have no three n H three, 23 00:01:54.239 --> 00:01:58.719 n I three N S three, p O three, p 24 00:01:58.959 --> 00:02:04.120 H three, pc L three, s BO three, s b 25 00:02:04.480 --> 00:02:08.599 h three, s p c L three A s O 26 00:02:08.800 --> 00:02:13.199 three a s H three A s c L three, 27 00:02:13.520 --> 00:02:17.919 et cetera. And in the five atom group n O five, 28 00:02:18.520 --> 00:02:22.639 n H four O, n H four I, p O five, 29 00:02:23.400 --> 00:02:29.120 p H four i, et cetera. Without offering any hypothesis 30 00:02:29.159 --> 00:02:32.919 regarding the cause of this symmetrical grouping of atoms, it 31 00:02:33.039 --> 00:02:37.000 is sufficiently evident from the examples just given that such 32 00:02:37.039 --> 00:02:40.759 a tendency or law prevails, and that, no matter what 33 00:02:40.879 --> 00:02:44.800 the character of the uniting atoms may be, the combining 34 00:02:44.919 --> 00:02:48.280 power of the attracting element, if I may be allowed 35 00:02:48.319 --> 00:02:51.919 to term, is always satisfied by the same number of 36 00:02:51.960 --> 00:02:58.680 these atoms. End quote. He then proceeded to represent the 37 00:02:58.840 --> 00:03:03.560 organometallic compounds obtained by formulae, which brought out the analogy 38 00:03:03.680 --> 00:03:06.840 with the inorganic types from which they were thought to 39 00:03:06.919 --> 00:03:12.599 have been derived. From his work on the organometallic compounds, 40 00:03:12.759 --> 00:03:16.319 Franklin developed the doctrine of the valance of the elements, 41 00:03:16.759 --> 00:03:19.319 the germ of which may be recognized in much that 42 00:03:19.400 --> 00:03:23.400 has gone before, particularly in the law of multiple proportions, 43 00:03:23.840 --> 00:03:28.000 which stated that the elements show different yet definite stages 44 00:03:28.039 --> 00:03:33.080 in their combinations. The so called doctrine of the polybasic 45 00:03:33.240 --> 00:03:37.719 acids contributed materially to the development of ideas upon the 46 00:03:37.759 --> 00:03:43.400 subject of the saturation capacity of the atoms. Galusac, Gmelin, 47 00:03:43.599 --> 00:03:47.280 and others inclined to the assumption that the atoms of 48 00:03:47.319 --> 00:03:51.840 the various metallic oxides contained one atom of oxygen united 49 00:03:52.000 --> 00:03:55.960 to one atom of metal, and that these oxides combined 50 00:03:56.000 --> 00:04:01.360 with one atom of acid to form neutral salts. Versalius, 51 00:04:01.520 --> 00:04:06.439 also after sixteen twenty eight, considered that this combining proportion 52 00:04:06.680 --> 00:04:11.639 was the rule. However, by Thomas Graham's famous investigation of 53 00:04:11.719 --> 00:04:15.639 the phosphoric acids eighteen thirty three, it was shown that 54 00:04:15.759 --> 00:04:19.199 a view so simple as this, according to which almost 55 00:04:19.240 --> 00:04:24.519 every acid was looked upon as monobasic, was untenable. Graham 56 00:04:24.639 --> 00:04:29.519 proved that in the ortho pyro and metaphosphoric acids. For 57 00:04:29.680 --> 00:04:34.040 each atom of phosphorus pentoxide, there were three, two and 58 00:04:34.240 --> 00:04:38.959 one atoms of basic water, these latter being replaced by 59 00:04:39.000 --> 00:04:45.399 equivalent amounts of metallic oxides. The saturation capacities of these 60 00:04:45.439 --> 00:04:48.439 acids were in this way shown to be dependent upon 61 00:04:48.480 --> 00:04:52.480 the amounts of basic water which entered into their constitution. 62 00:04:53.560 --> 00:04:57.360 Libic extended this to many other acids and distinguished between 63 00:04:57.600 --> 00:05:02.399 mono die and tribasic acid, and the property was referred 64 00:05:02.439 --> 00:05:06.399 to as the basicity of the atoms, a term which, 65 00:05:06.759 --> 00:05:10.319 with the ideas inherent in it, clung for some time 66 00:05:10.439 --> 00:05:14.959 to the theory of valence. In eighteen fifty seven, for example, 67 00:05:15.199 --> 00:05:21.480 the terms vasicity, valancy, and atomicity were used as synonymous 68 00:05:21.839 --> 00:05:24.560 and as the measure of the number of hydrogen atoms 69 00:05:24.560 --> 00:05:29.399 that could be replaced or held in combination. The idea 70 00:05:29.519 --> 00:05:34.480 of basicity was soon extended to the compound organic radicals. 71 00:05:34.959 --> 00:05:38.920 In eighteen fifty five, C A voltz eighteen seventy to 72 00:05:39.000 --> 00:05:43.480 eighteen eighty four, a pupil of Libic and Duma showed 73 00:05:43.560 --> 00:05:47.920 that glycerine C three H eight O three may be 74 00:05:48.040 --> 00:05:52.160 regarded as the hydrate of the radical C three H five. 75 00:05:53.199 --> 00:05:57.360 Four years previous, A. W. Williamson eighteen twenty four to 76 00:05:57.480 --> 00:06:01.000 nineteen O four had expressed the VW that a large 77 00:06:01.079 --> 00:06:04.399 number of compounds may be referred to the type of water, 78 00:06:04.959 --> 00:06:09.480 the monobasic acids to one molecule, and the polybasic acids, 79 00:06:09.800 --> 00:06:14.199 which are of greater molecular complexity, to a condensed water type. 80 00:06:15.079 --> 00:06:20.959 He wrote, C two H three O H O equals 81 00:06:21.399 --> 00:06:27.160 acetic acid, s O two H two O two equals 82 00:06:27.480 --> 00:06:33.000 sulfuric acid. Words now showed that the composition of glycerine 83 00:06:33.000 --> 00:06:37.240 could be represented by the formula C three H five 84 00:06:37.560 --> 00:06:42.360 three prime H three O three, which was similar to 85 00:06:42.399 --> 00:06:46.160 the formula by which, in accordance with the ideas of Williamson, 86 00:06:46.720 --> 00:06:51.800 ordinary phosphoric acid P O three prime H three O 87 00:06:52.000 --> 00:06:58.199 three was represented. Gerhardt, in his Trete de chimi organique 88 00:06:58.560 --> 00:07:04.399 stated that quote, in order to compare the radicals among themselves, 89 00:07:04.519 --> 00:07:07.879 I proposed to refer them all to the radical of hydrogen, 90 00:07:08.480 --> 00:07:14.079 and consequently I name them monotomic, diatomic triatomic according to 91 00:07:14.160 --> 00:07:17.879 the quantity of hydrogen which they are capable of replacing 92 00:07:18.000 --> 00:07:21.920 in the type H two O, that is, according to 93 00:07:21.959 --> 00:07:26.199 whether they are equivalent to one, two, or three atoms 94 00:07:26.199 --> 00:07:30.199 of hydrogen. So, for instance, in alcohol and in ether 95 00:07:31.360 --> 00:07:36.800 o C two H five oh C two H five 96 00:07:37.160 --> 00:07:42.120 o C two H five C two H five, the 97 00:07:42.240 --> 00:07:47.519 radical ethyl is monotomic because it replaces H one atom 98 00:07:47.560 --> 00:07:54.199 of hydrogen in the type water end quote. The terms 99 00:07:54.439 --> 00:07:59.360 monotomic and polyatomic had been employed much earlier, but in 100 00:07:59.399 --> 00:08:06.639 a difference. Thus, in eighteen twenty seven, Presalius called fluorine chlorine, 101 00:08:06.680 --> 00:08:12.160 et cetera polyatomic because several atoms of these halogens unite 102 00:08:12.240 --> 00:08:16.720 with a single atom of another element. In eighteen thirty three, 103 00:08:17.160 --> 00:08:20.720 Gordon des Sante used the same terms to express the 104 00:08:20.800 --> 00:08:24.000 number of atoms in a molecule, in which sense they 105 00:08:24.040 --> 00:08:29.639 were used by Kameelin, Clausius and Odling. Williamson attached the 106 00:08:29.680 --> 00:08:33.759 idea of capacity for saturation or atomicity of the radical, 107 00:08:34.120 --> 00:08:38.000 to the number of hydrogen atoms capable of substitution, and 108 00:08:38.080 --> 00:08:41.480 the notion of atomicity was soon extended to the known 109 00:08:41.600 --> 00:08:45.679 compound radicals and played an important part in the theory 110 00:08:45.759 --> 00:08:53.000 of types et cetera, which obtained inorganic chemistry. Franklin's speculations 111 00:08:53.080 --> 00:08:57.039 concerning the substitution value of radicals compared with that of 112 00:08:57.120 --> 00:09:01.480 elementary atoms were of great importance, yet they did not 113 00:09:01.639 --> 00:09:06.279 meet with immediate approval. By eighteen fifty eight, however, the 114 00:09:06.399 --> 00:09:11.240 valence theory had made rapid progress. In this year, August 115 00:09:11.399 --> 00:09:16.759 Kekule first deduced the balance of carbon from its simplest compounds, 116 00:09:16.799 --> 00:09:21.639 declaring it to be tetravalent. This had already been recognized 117 00:09:21.679 --> 00:09:26.000 by Colbert and Franklin, if not expressly stated by them, 118 00:09:26.360 --> 00:09:30.200 But Caculae rendered further and much greater service by inquiring 119 00:09:30.240 --> 00:09:32.759 into the manner in which two or more of these 120 00:09:32.840 --> 00:09:37.759 tetravalent carbons were united with one another. The doctrine of 121 00:09:37.799 --> 00:09:42.320 atomic chains open and closed sprang from this, and the 122 00:09:42.360 --> 00:09:47.480 domination of the structural idea in chemistry became complete. In 123 00:09:47.559 --> 00:09:52.000 the same year, and independently of Caculae, M. S. Cupere 124 00:09:52.360 --> 00:09:57.720 arrived at conclusions almost identical with those of Caculae. Both 125 00:09:57.799 --> 00:10:03.080 Caculae and Couperre expressed with absolute definiteness the axiom that 126 00:10:03.320 --> 00:10:06.919 the atomicity of the elements was to be made use 127 00:10:06.960 --> 00:10:11.600 of for arriving at the constitution of chemical compounds. The 128 00:10:11.639 --> 00:10:15.279 idea of the term atomicity had without any doubt been 129 00:10:15.320 --> 00:10:20.480 introduced by Franklin six years previous to this. The further 130 00:10:20.519 --> 00:10:24.120 development of the above axiom and its utilization in the 131 00:10:24.120 --> 00:10:27.720 theory of the linking of atoms, was carried out mainly 132 00:10:27.799 --> 00:10:31.679 by Caculae, and in the succeeding years also by Butlerrow 133 00:10:31.960 --> 00:10:37.200 and erlen Meyer. While the radical and type theories were 134 00:10:37.240 --> 00:10:41.320 attempts at securing an idea of the structure of chemical compounds, 135 00:10:41.799 --> 00:10:44.960 it was the valance theory which rendered it possible to 136 00:10:45.000 --> 00:10:47.639 furnish a lucid answer to the question as to the 137 00:10:47.679 --> 00:10:53.039 composition of such bodies, and especially after the year eighteen seventy, 138 00:10:53.600 --> 00:10:57.679 the determination of the constitution of complex molecules became the 139 00:10:57.759 --> 00:11:03.799 higher aim of chemistry. Some rudiments of systematic classification had 140 00:11:03.840 --> 00:11:09.120 before this been introduced into organic chemistry, and these classificatory 141 00:11:09.240 --> 00:11:13.360 beginnings were of great assistance in the erection of structural chemistry. 142 00:11:14.399 --> 00:11:18.000 In eighteen thirty six, Laurent, when he brought forward his 143 00:11:18.159 --> 00:11:23.320 nucleus series, arranged organic compounds in series. And it was 144 00:11:23.320 --> 00:11:26.840 in eighteen forty one that Gerhardt entered on a research 145 00:11:26.960 --> 00:11:30.480 to discover some general law which might suggest an all 146 00:11:30.559 --> 00:11:34.840 sufficing system of classification, and the following year he was 147 00:11:34.879 --> 00:11:38.559 ready with his letder of combustion, with its highest drung 148 00:11:38.679 --> 00:11:44.080 cerebral matter, its lowest carbonic acid, water and ammonia, to 149 00:11:44.240 --> 00:11:49.799 unfold the whole science of organic chemistry. He soon found, however, 150 00:11:50.279 --> 00:11:54.639 that this arrangement, according to mere complexity of composition, was 151 00:11:54.679 --> 00:11:59.240 no sufficient classification. So he betook himself to another line 152 00:11:59.279 --> 00:12:03.039 of inquiry. A note of triumph seems to ring through 153 00:12:03.080 --> 00:12:06.480 the following lines from the preface to his Precis de 154 00:12:06.559 --> 00:12:12.399 schimik Organique, published in eighteen forty four. Quote, I have 155 00:12:12.480 --> 00:12:17.879 succeeded in establishing homologous series. These have indicated to me 156 00:12:18.000 --> 00:12:22.480 the means of classifying organic substances in natural families, and 157 00:12:22.600 --> 00:12:26.559 of disposing them on a kind of combustion letter end. 158 00:12:28.480 --> 00:12:30.720 As a matter of fact, it was only the word 159 00:12:30.960 --> 00:12:36.320 homology that Gerhard could claim as his own. Two years earlier, J. 160 00:12:36.559 --> 00:12:40.320 Shield had shown that a very simple relation existed between 161 00:12:40.320 --> 00:12:43.919 the alcohols, then known that their radicals might all be 162 00:12:44.039 --> 00:12:49.120 represented by the general expression n R plus h R, 163 00:12:49.320 --> 00:12:54.879 suggesting the group C two H two C equal six. Moreover, 164 00:12:55.039 --> 00:12:58.440 in the same year, Duma had demonstrated the existence of 165 00:12:58.480 --> 00:13:01.720 a similar relation between the several members of the fatty 166 00:13:01.759 --> 00:13:06.159 acids known to him. Yet Gerr had generalized from this 167 00:13:06.320 --> 00:13:10.399 fact of homology and proved the possibility of predicting the 168 00:13:10.440 --> 00:13:16.080 existence of terms unknown in his series. Many systems of 169 00:13:16.159 --> 00:13:21.320 classification were suggested during the sixth decade, the classification by 170 00:13:21.440 --> 00:13:25.039 series as that of Shield and duma, that of series 171 00:13:25.080 --> 00:13:30.399 depending upon formulae, series depending upon chemical behavior, and many 172 00:13:30.440 --> 00:13:35.679 other systems. The lack of agreement among chemists, however, as 173 00:13:35.720 --> 00:13:39.320 to the formulae belonging to the different compounds, as to 174 00:13:39.360 --> 00:13:43.159 the relative weights of the molecules, the atomic weights, and 175 00:13:43.279 --> 00:13:47.399 even the number of atoms, prevented a general acceptance of 176 00:13:47.480 --> 00:13:52.559 any of the classifications proposed until Caculae established the fact 177 00:13:52.639 --> 00:13:56.279 of the tetravalance of the carbon atom, showed the difference 178 00:13:56.320 --> 00:14:02.799 between saturated and unsaturated compounds, and reduced his chain formulae. 179 00:14:03.399 --> 00:14:08.799 About eighteen sixty Franklin's views regarding a saturation capacity peculiar 180 00:14:08.840 --> 00:14:13.879 to the elements were accepted either delitescently or expressly by 181 00:14:13.919 --> 00:14:18.440 most chemists, but it was considered that this saturation capacity, 182 00:14:18.759 --> 00:14:23.679 under certain circumstances might be a varying one. In eighteen 183 00:14:23.720 --> 00:14:28.440 fifty six, Gerhardt had stated that nitrogen was sometimes triatomic 184 00:14:28.799 --> 00:14:35.159 and sometimes pentatomic. This view was also held by Franklin, Vts. Williamson, 185 00:14:35.240 --> 00:14:39.200 and Coupert, and the latter three considered that the valance 186 00:14:39.320 --> 00:14:42.759 was also variable in the cases of many other elements. 187 00:14:43.559 --> 00:14:46.879 Corbet thought that it must be assumed that a constant 188 00:14:46.919 --> 00:14:50.879 valancy was characteristic of a few elements, and a varying 189 00:14:51.000 --> 00:14:54.639 one characteristic of many more, since he perceived in it 190 00:14:54.759 --> 00:14:58.799 another expression for the law of multiple proportions, and nothing 191 00:14:58.919 --> 00:15:02.720 was known concerning the cause of valence. As early as 192 00:15:02.720 --> 00:15:07.320 eighteen fifty four, Colbert had concluded that each element possessed 193 00:15:07.320 --> 00:15:11.840 a maximum saturation capacity, but that lower stages of saturation 194 00:15:12.080 --> 00:15:15.679 might exist along with this, and toward the beginning of 195 00:15:15.720 --> 00:15:19.480 the sixties several chemists who took an active part in 196 00:15:19.519 --> 00:15:23.639 developing the structure theory expressed the same opinion in a 197 00:15:23.679 --> 00:15:29.799 more definite manner. Allenmeyer, in particular, maintained in various papers 198 00:15:30.039 --> 00:15:34.440 and afterward in his leabug dea organishan Kimi that each 199 00:15:34.559 --> 00:15:38.879 element possesses a maximum valancy, or that each is furnished 200 00:15:38.919 --> 00:15:45.240 with a definite number of affinivalentin or affinity points affinitetspunkten. 201 00:15:45.879 --> 00:15:49.679 Only part of these, however, being in many cases combined 202 00:15:49.720 --> 00:15:54.919 with the affinity points of other elements. Calculates theory of 203 00:15:55.000 --> 00:15:58.440 the constant balance of the elements could not withstand the 204 00:15:58.480 --> 00:16:02.559 critical examinations to which it was subjected. However, and in 205 00:16:02.639 --> 00:16:05.559 the course of the last forty years, the majority of 206 00:16:05.679 --> 00:16:09.000 chemists have adopted the view that the atoms of most 207 00:16:09.039 --> 00:16:13.919 of the elements possess a varying saturation capacity, varying according 208 00:16:14.000 --> 00:16:19.559 to the conditions. Although the structure theory was unable to 209 00:16:19.600 --> 00:16:23.159 accomplish the extreme expectations which aimed at a knowledge of 210 00:16:23.200 --> 00:16:27.279 the special arrangement of the atoms, it possessed nonetheless great 211 00:16:27.399 --> 00:16:32.200 practical value. The development of organic chemistry since the middle 212 00:16:32.240 --> 00:16:35.799 of the sixth decade shows in fact that through the 213 00:16:35.840 --> 00:16:39.639 aid of the structural hypothesis, the discovery of new modes 214 00:16:39.679 --> 00:16:43.960 of formation and decomposition of compounds, the recognition of the 215 00:16:44.039 --> 00:16:49.360 relations existing between various classes of bodies, and especially the 216 00:16:49.399 --> 00:16:54.399 interpretation of the constitution of numerous organic substances became possible. 217 00:16:55.360 --> 00:16:59.720 Calculates theory of the aromatic compounds forms the most striking 218 00:16:59.759 --> 00:17:04.440 proof of this in eighteen sixty five to eighteen sixty six. 219 00:17:04.839 --> 00:17:09.559 Taking the quadryvalance of carbon as his principle, Calculate called 220 00:17:09.599 --> 00:17:12.759 attention to the fact that in the fatty compounds, the 221 00:17:12.839 --> 00:17:16.359 carbon atoms are linked together by one balance of each. 222 00:17:17.400 --> 00:17:20.839 In the case of benzene, the next simplest assumption was 223 00:17:20.880 --> 00:17:24.359 made in accordance with which the carbon atoms are linked 224 00:17:24.400 --> 00:17:28.400 together by one and two balances alternately, so as to 225 00:17:28.480 --> 00:17:32.319 form a closed chain or ring. Of the twenty four 226 00:17:32.359 --> 00:17:36.599 affinities of the six carbon atoms, eighteen are employed in 227 00:17:36.720 --> 00:17:41.400 linking carbon to carbon. Thus six over two times four 228 00:17:41.559 --> 00:17:48.039 plus six over two times two equals eighteen. Six valencies 229 00:17:48.119 --> 00:17:51.680 then remain which are satisfied by the six hydrogen atoms 230 00:17:51.720 --> 00:17:56.559 of the benzene. Hence, according to Calculate, benzene may be 231 00:17:56.640 --> 00:18:00.480 represented by means of a regular hexagon whose sides are 232 00:18:00.519 --> 00:18:04.359 composed of single and of double lines alternately, the c 233 00:18:04.920 --> 00:18:11.920 groups occupying the corners. Thus, Caculae and his pupils, together 234 00:18:12.039 --> 00:18:15.200 with many other chemists, who had busied themselves with the 235 00:18:15.240 --> 00:18:19.400 derivatives of benzene after this view had been published, now 236 00:18:19.480 --> 00:18:23.160 directed their efforts to comparing all the known and rapidly 237 00:18:23.279 --> 00:18:27.599 increasing observations bearing upon this class of bodies. With the 238 00:18:27.680 --> 00:18:32.119 deductions drawn from the above formula and therewith to proving 239 00:18:32.240 --> 00:18:36.240 by actual experiment the admissibility of the assumptions on which 240 00:18:36.279 --> 00:18:41.759 the formula was based. The result was that Caculae's anticipations 241 00:18:41.799 --> 00:18:48.079 were realized and his hypothesis substantiated. In eighteen sixty six, 242 00:18:48.240 --> 00:18:53.039 Caculae had stated that what is wanted is that the 243 00:18:53.160 --> 00:18:57.680 largest possible number of substitution products of benzene should be 244 00:18:57.720 --> 00:19:01.279 prepared by the most diverse methods, that they should be 245 00:19:01.440 --> 00:19:06.400 most carefully compared with regard to isomerism, that the modifications 246 00:19:06.480 --> 00:19:11.799 so found should be counted end quote. And in the 247 00:19:11.839 --> 00:19:15.640 eighteen sixty seven edition of his textbook he called attention 248 00:19:15.759 --> 00:19:18.839 to a number of cases of isomerism which at that 249 00:19:19.039 --> 00:19:23.720 time had received no explanation. Among these we find that 250 00:19:23.839 --> 00:19:30.480 of ethylene chloride with ethylidne chloride, of acetyl with diethyl 251 00:19:30.599 --> 00:19:36.519 glycol for malaic and fiumaric for ucake and saccharic acids. 252 00:19:36.960 --> 00:19:40.039 The last effort of his philosophy had only found him 253 00:19:40.079 --> 00:19:44.640 the two formula C four H two double prime O 254 00:19:44.799 --> 00:19:50.359 two H two O two and C six H eight 255 00:19:50.640 --> 00:19:57.079 double prime O six H two O two, respectively. Calculae 256 00:19:57.240 --> 00:20:01.359 instanced two those bodies which only differed in their effect 257 00:20:01.519 --> 00:20:06.880 on polarized light, the tartaric, the malic and camphoric acids, 258 00:20:06.920 --> 00:20:11.720 and the amyl alcohols. It was owing to these cases 259 00:20:11.759 --> 00:20:16.680 of isomerism that structural formulae could not be assigned. In 260 00:20:16.680 --> 00:20:19.880 some cases, a greater number of isomeric bodies were known 261 00:20:19.960 --> 00:20:23.079 than could possibly be accounted for by any arrangement of 262 00:20:23.119 --> 00:20:27.519 the atoms in formulae upon a plane's surface, retaining, of course, 263 00:20:27.960 --> 00:20:31.559 the accepted views as to balance, et cetera. And since 264 00:20:31.640 --> 00:20:36.559 these isomers differed principally in certain physical properties, they were 265 00:20:36.599 --> 00:20:41.680 at first termed physical isomers. The study of these resulted 266 00:20:41.720 --> 00:20:44.839 in the consideration of the arrangement of atoms in space, 267 00:20:45.400 --> 00:20:50.079 the chemistry of space, or stereochemistry, in which branch of 268 00:20:50.160 --> 00:20:53.640 the science an extended view of atomic grouping was essayed. 269 00:20:54.880 --> 00:21:00.839 Modern stereochemistry was anticipated by Emmanuel Swedenborg in seventy twenty one, 270 00:21:01.359 --> 00:21:04.079 when he made an attempt to explain the phenomena of 271 00:21:04.160 --> 00:21:10.039 chemistry and physics on geometrical principles. In his prodromus principorium 272 00:21:10.160 --> 00:21:17.839 rerum naturalium. Seeven novorum tentaminum, chemium at physicum, experimentalem geometric 273 00:21:18.119 --> 00:21:23.240 explicandi and similar beginnings were made by Johann Barcussen ten 274 00:21:23.319 --> 00:21:29.119 years earlier. In eighteen sixty four, Carrius, who first used 275 00:21:29.119 --> 00:21:35.720 the term physical isomerism, explained it as follows quote. I 276 00:21:35.799 --> 00:21:38.759 have tentatively expressed a view as to the cause of 277 00:21:38.799 --> 00:21:44.720 what I call physical isomerism. Substances which exhibit this property 278 00:21:45.319 --> 00:21:49.519 yield under the same or nearly the same conditions, products 279 00:21:49.559 --> 00:21:54.680 which are either identical or physically isomeric. According to our 280 00:21:54.759 --> 00:21:58.599 present views, I think it improbable that such substances should 281 00:21:58.599 --> 00:22:02.400 have their atoms differently arranged, that is, that they should 282 00:22:02.400 --> 00:22:06.480 be metameric. But it is quite conceivable that in the 283 00:22:06.559 --> 00:22:11.000 formation of physical isomers, differences of condition may cause the 284 00:22:11.079 --> 00:22:15.039 production of substances with the same arrangement of the atoms 285 00:22:15.079 --> 00:22:19.480 within the molecule, but with a different aggregation of these molecules, 286 00:22:20.160 --> 00:22:25.240 and that thereon depends the difference in their properties. Thus 287 00:22:25.640 --> 00:22:30.079 we must consider as certainly only physically isomeric, a large 288 00:22:30.160 --> 00:22:33.519 number of the substances distinguished by the difference of their 289 00:22:33.559 --> 00:22:37.599 action on polarized light, such as the two modifications of 290 00:22:37.839 --> 00:22:42.799 amyl alcohol, the tartaric acids, the malic acids, et cetera. 291 00:22:44.240 --> 00:22:51.400 End this explanation was inadequate, and in eighteen seventy three 292 00:22:51.720 --> 00:22:56.319 Johannes Vivalentius eighteen thirty five to nineteen oh two, who 293 00:22:56.440 --> 00:23:00.319 succeeded Colbert as professor of chemistry at Leipzig in eighteen 294 00:23:00.359 --> 00:23:05.839 eighty five, suggested the substitution of the term geometrical isomerism 295 00:23:06.200 --> 00:23:10.880 for physical isomerism. He had been engaged in an investigation 296 00:23:11.000 --> 00:23:15.039 of the various modifications of lactic acid, and had found 297 00:23:15.240 --> 00:23:20.200 that the ethylene lactic acid or hydrocrylic acid prepared by 298 00:23:20.240 --> 00:23:26.079 Bielstein by treating beta iodopropionic acid with silver oxide, possessed 299 00:23:26.119 --> 00:23:30.160 properties different from those of the ethylene lactic acid obtained 300 00:23:30.160 --> 00:23:35.039 from ethylene cyane hydrone. This difference was so marked that 301 00:23:35.079 --> 00:23:38.079 he thought it might be explained by assigning the two 302 00:23:38.160 --> 00:23:44.119 acids different structural formulae. The first was optically inactive, while 303 00:23:44.160 --> 00:23:49.319 the second, paralactic acid, was textra rotary. This one point 304 00:23:49.400 --> 00:23:53.480 of difference appeared hardly sufficient to make it necessary to 305 00:23:53.559 --> 00:23:58.160 assign to paralactic acid a structural formula other than that 306 00:23:58.240 --> 00:24:03.119 of fermentation lactic acid. It seemed much more likely that here, 307 00:24:03.240 --> 00:24:06.599 at any rate, were cases of what Carriers had called 308 00:24:06.839 --> 00:24:12.839 physical but what Wislicenus now proposed to call geometrical isomerism. 309 00:24:13.880 --> 00:24:18.039 He said, quote my conclusion for the present is to 310 00:24:18.119 --> 00:24:22.759 declare paralactic acid and the fermentation lactic acid as most 311 00:24:22.880 --> 00:24:28.759 probably only geometrically isomeric. Their great similarity, even identity in 312 00:24:28.880 --> 00:24:33.240 all chemical properties, the ease of transformation on heating of 313 00:24:33.319 --> 00:24:37.279 the first into the second, and their differences, particularly in 314 00:24:37.319 --> 00:24:41.519 optical behavior, may all alike be explained on this basis. 315 00:24:42.599 --> 00:24:46.799 Concerning the special how of this explanation, I am engaged 316 00:24:46.839 --> 00:24:55.039 in experimental investigations. The next year ja fand Hoff furnished 317 00:24:55.079 --> 00:24:59.880 an answer to this. However, before giving his exposition, mention 318 00:25:00.200 --> 00:25:03.240 must be made of Luis Pasteurs eighteen twenty two to 319 00:25:03.319 --> 00:25:08.640 eighteen ninety five, pioneer work in this field. Pasta studied 320 00:25:08.680 --> 00:25:13.279 the various tartrates crystallographically and showed that there are four 321 00:25:13.400 --> 00:25:20.240 isomeric tartaric acids, that is, rhsemic acid, inactive tartaric acid, 322 00:25:20.680 --> 00:25:25.640 and right and left rotating tartaric acids. He showed moreover 323 00:25:26.079 --> 00:25:29.480 that the two latter acids crystallized in similar but in 324 00:25:29.599 --> 00:25:35.160 oppositely built up and antiomorph forms, that they both rotate 325 00:25:35.240 --> 00:25:38.680 a ray of polarized light through equal angles but in 326 00:25:38.720 --> 00:25:43.119 opposite senses, and that when mixed in equal quantities, they 327 00:25:43.200 --> 00:25:49.200 yield optically inactive rhsemic acid. Further, he succeeded in decomposing 328 00:25:49.279 --> 00:25:53.839 rhsemic acid again into the two optically active tartaric acids 329 00:25:54.119 --> 00:25:59.960 by three different methods. Pasta established the correlation of molecul 330 00:26:00.119 --> 00:26:04.440 ll dysymmetry and rotary power in these investigations, and it 331 00:26:04.519 --> 00:26:08.799 remained to discover under which conditions the dysymmetry could obtain 332 00:26:08.880 --> 00:26:14.519 in two molecules structurally identical. This was undertaken in eighteen 333 00:26:14.559 --> 00:26:18.720 seventy four by J. A. Fantauff in Holland and J. A. 334 00:26:18.920 --> 00:26:23.279 Lebel in France, who, in papers published that year, offered 335 00:26:23.279 --> 00:26:27.720 an explanation practically the same for cases of isomerism which 336 00:26:27.759 --> 00:26:30.559 could not be included under the theories of the time. 337 00:26:31.559 --> 00:26:35.759 Fantauff states that in general Lebel's original paper and his 338 00:26:36.079 --> 00:26:40.240 were in accord, but that while Paste's researches formed Lebel's 339 00:26:40.279 --> 00:26:44.000 starting point he took for his own caculaise laws of 340 00:26:44.039 --> 00:26:48.119 the tetravealence of carbon, to which he added the hypothesis 341 00:26:48.519 --> 00:26:51.720 that the four balancies are directed toward the corners of 342 00:26:51.720 --> 00:26:55.640 the tetrahedron, in the center of which is the carbon atom. 343 00:26:56.200 --> 00:27:01.359 To quote from Foynd's study of chemical composition quote font 344 00:27:01.359 --> 00:27:06.000 Hoff introduced no fundamental change in or addition to the 345 00:27:06.039 --> 00:27:11.799 original Valiancy hypothesis. A two dimensional representation of molecular structure 346 00:27:11.839 --> 00:27:14.839 could not at any time have been considered as really 347 00:27:15.000 --> 00:27:18.680 true to the actual occurrence, but it was legitimate to 348 00:27:18.839 --> 00:27:22.119 use it because of its greater simplicity, as long as 349 00:27:22.160 --> 00:27:26.319 it proved adequate to the purpose. And with this recognition 350 00:27:26.400 --> 00:27:30.480 and restriction, we continue to use plain structural formulae in 351 00:27:30.559 --> 00:27:36.319 the majority of cases. End font Hoff. Following up the 352 00:27:36.400 --> 00:27:40.240 suggestion that may be found implied in Pastor's paper and 353 00:27:40.359 --> 00:27:45.319 that was explicitly stated by Weslycenius, introduces into the science 354 00:27:45.400 --> 00:27:50.039 the consideration of the arrangement of atoms in space. Quote. 355 00:27:50.480 --> 00:27:56.440 Stereochemistry from stereos solid in the restricted sense of the word, 356 00:27:56.759 --> 00:28:01.000 comprises chemical phenomena which demand a considerate of the grouping 357 00:28:01.039 --> 00:28:07.119 of atoms in space end quote. Carbon compounds only were 358 00:28:07.160 --> 00:28:10.640 considered at first, but the scope of the phenomena dealt 359 00:28:10.640 --> 00:28:14.440 with has been extended and now includes compounds of tribalent 360 00:28:14.599 --> 00:28:20.440 and pentavalent, nitrogen, of tin, and of sulfur. Font Hoff's 361 00:28:20.480 --> 00:28:25.200 theory of the asymmetric carbon atom, however, met with difficulties 362 00:28:25.240 --> 00:28:30.279 on its annunciation. To quote from F. P. Armitage's History 363 00:28:30.319 --> 00:28:36.279 of Chemistry quote, When Fantoff enunciated his theory of the 364 00:28:36.359 --> 00:28:40.200 asymmetric carbon atom, he was able to say, with much 365 00:28:40.279 --> 00:28:44.559 show of truth, that all optically active substances did contain 366 00:28:44.680 --> 00:28:50.559 certainly one such atom. Soon, however, were heard dissentient voices. 367 00:28:51.279 --> 00:28:56.440 What of propyle alcohol, asked one, and of styrolene, demanded another. 368 00:28:57.359 --> 00:29:01.519 The propyle alcohol owes its activity to pis of amyl alcohol, 369 00:29:01.839 --> 00:29:06.400 answered Henniger. The styrrolene is impure, said fant Hoff, and 370 00:29:06.480 --> 00:29:11.000 their evidence was irrefutable. But font Hoff could not, in 371 00:29:11.039 --> 00:29:15.400 eighteen seventy four maintain that the presence of one asymmetric 372 00:29:15.480 --> 00:29:21.400 carbon atom necessarily implied optical activity for secondary amyl alcohol 373 00:29:21.480 --> 00:29:27.200 and its derivatives, also propylene alcohol, were certainly inactive, yet 374 00:29:27.279 --> 00:29:33.160 all contained an asymmetric carbon atom. The problem, said the stereochemists, 375 00:29:33.160 --> 00:29:36.599 were somewhat similar to that of the relation between tartaric 376 00:29:36.680 --> 00:29:41.240 and drassemic acid, so happily solved years before by Pasteur. 377 00:29:42.119 --> 00:29:45.440 His methods were recalled, and le Bell soon showed that 378 00:29:45.519 --> 00:29:49.559 these inactive bodies were in reality mixtures of two optically 379 00:29:49.640 --> 00:29:55.039 opposite isomers, and others helping that indeed, every substance with 380 00:29:55.160 --> 00:30:00.440 but one asymmetric carbon atom was equally capable of mesotomis. 381 00:30:01.519 --> 00:30:05.279 The four varieties of tartaric acid had offered no difficulty 382 00:30:05.880 --> 00:30:10.680 with two asymmetric carbon atoms similarly habited, there was necessarily 383 00:30:10.799 --> 00:30:15.720 neutralization or a duplication of optical activity. But where two 384 00:30:15.920 --> 00:30:20.799 or more carbon atoms occurred asymmetric by union with different radicals, 385 00:30:21.119 --> 00:30:24.799 as in the sugars and their derivatives, many more cases 386 00:30:24.799 --> 00:30:29.279 of physical isomerism suggested themselves and have since been verified 387 00:30:30.160 --> 00:30:34.680 without doubt. The asymmetric carbon atom has made a triumphant progress, 388 00:30:35.079 --> 00:30:38.000 winning for Lebel the JACA price of eighteen eighty one, 389 00:30:38.480 --> 00:30:42.160 for Fantoefe dominant voice, and the scientific councils of the world. 390 00:30:42.839 --> 00:30:46.039 It will rank with the phlogiston of Starr. The oxygen 391 00:30:46.079 --> 00:30:49.640 of La Boisier, the atom of Dalton, and the dualism 392 00:30:49.720 --> 00:30:56.799 of Beerzalius. Among the most noted workers in the field 393 00:30:56.839 --> 00:31:02.200 of stereochemistry have been Aphon Baya, Ballach, Victor Maya, Rique 394 00:31:02.519 --> 00:31:08.799 bischof Werner, Hantsch, Hours and Overton. Even now, the subject 395 00:31:08.880 --> 00:31:12.880 is in its infancy, and stereochemical theories are as yet 396 00:31:12.960 --> 00:31:16.200 insufficiently advanced to present a clear view of the question 397 00:31:16.279 --> 00:31:22.960 of geometrical isomerism. Yet, as Ladenburg has said quote, it 398 00:31:23.039 --> 00:31:27.079 is beyond doubt that the founding and development of stereochemistry, 399 00:31:27.400 --> 00:31:31.119 a name which originated with Victor Maya, is the most 400 00:31:31.119 --> 00:31:34.720 important thing that was accomplished in organic chemistry during the 401 00:31:34.799 --> 00:31:40.039