Abstract
In the preceding paper, nitrogenous bases were divided into two classes according as the first amino-absorption band, which they exhibit at about 2200 A, do or do not contribute to the optical activity of the molecules. Thus, for spiro heptane-diamine, the absorption spectrum showed a rapid rise in intensity caused by the presence in the molecule of two lone-pairs of electrons associated with the nitrogen atoms. On neutralization of the base, this strong absorption at 2300 A disappeared, but the rotatory dispersion remained almost unchanged. For both base and salt the active absorption region was between 1950 and 1400 A, and the bands of the amine at longer wave-lengths were not circularly dichroic. A test of the conditions prevailing in any particular case was specified on the basis of the behaviour of the specific rotaion on neutralization, since, when a large change of mangnitude or sign occurs, the bands of longer wave-length must play an important role. Care is necessary in the use of this rule, because solvents such as water may co-ordinate with the amine, causing the behaviour of the free base to resemble that of its salts. When, however, a non-polar solvent is used for the base, and the change is observed, it is practically certain that interpretation is correct. In the present paper, a detailed account is given of the corresponding phenomenon as shown by a base whose optical properties are more typical of this class of compounds, namely, secondary butylamine: CH 3 -C-C 2 H 5 -NH 2 -H The effects of neutralization have already been discussed by rule (1930), but his attention was confined to the relationship between polarity and rotatory power, and the question of circularly dichroic absorption bands was ignored. Since, however, Polarity is usually manifested in the groups with absorption bands nearest to the visual region, the two arguments run to some extent parallel to one another, but the present point of view is more fundamental.
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Schedule a callMore From: Proceedings of the Royal Society of London. Series A - Mathematical and Physical Sciences
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