Barriers to rotation about the CN bond in several unusual thioamides have been studied with 100 MHz 1 H-NMR spectroscopy. This rotation is still frozen at 170°C in p -chlorophenylglyoxylthiomorpholide ( 2 ) in DMSO-d 6 . NMR spectra and the IR carbonyl frequencies show that 2b and 2c are the most important resonance forms, the latter making a significant contribution to the bonding in the transition state. The high rotational barrier is related to preferential stabilization of the ground state by the opposed orientation of two parallel dipoles ( 2b ). In the sterically crowded molecules 4–(2′-hydroxythiobenzoyl)morpholine ( 3 ) and 1–(2′-hydroxythiobenzoyl)piperidine ( 4 ) rapid ring inversion between two chair forms of slightly different energy superimposed on the much slower rotation about the CN bond implies that only a mean value for the rotational barrier height can be obtained experimentally.

The far-infrared spectra in the region of 50 to 400 cm−1 are reported for the vapours of methylenecyclohexane and the related compounds 4-methylenetetrahydro-4H-pyran, 4-methylenetetrahydro-4H-thiopyran and 3-methylenetetrahydro-4H-pyran. The absorptions are assigned to the three out-of-plane deformations of the six-membered rings. The observed series of Q branches are ascribed to combination sequences involving the three modes. The lowest wavenumber sequence in each compound is believed to arise from a vibration which if completely executed would take the chair conformation to its equivalent via an inversion through the planar form. With the use of a one-dimensional Hamiltonian incorporating a quadratic-quartic double minimum potential function, barriers to planarity for the rings are estimated. The similarities between these compounds and the corresponding ketones are discussed.

Raman spectra of aqueous solutions of dimethylsulfoxide, dimethylsulfoxide-d6, acetone and acetonitrile are reported in the OH stretching region, and in the stretching regions of the functional groups of these solutes. Raman intensities and frequency shifts of these bands show definite trends with varying concentrations of the solutions. The results obtained are discussed in terms of the mixture model of water, and they are compared with results obtained from Raman spectral studies of aqueous electrolytes. It is proposed that water structure breaking and the formation of solute-solvent complexes when organic solutes are added to water can account for these results.

The integrated intensities, frequencies, and half-band widths of the fundamental symmetric and asymmetric NH2 stretching vibrations in 33 ortho-substituted anilines, measured in dilute carbon tetrachloride solution, have been examined in relation to the corresponding absorption band parameters for 31 meta- and para-substituted anilines, taking into consideration the electronic effects of the substituents. From an almost tetrahedral configuration in p-phenylenediamine, the calculated s-character of the nitrogen atom gradually increases as the substituent groups become more electron withdrawing, with a resultant increase in the apparent HNH angle and the NH force constant. Ortho substitution in general leads to enhanced HNH angle opening, probably because of intramolecular hydrogen bonding. The decrease in half-band width for both vibrational modes in ortho-substituted anilines with respect to corresponding values in meta and para compounds is ascribed to steric hindrance to solvation of the amino group.The asymmetric intensities in ortho-substituted anilines are generally increased over corresponding values in meta and para compounds, unlike the behavior of the symmetric mode. These results are consistent with a vibrational mechanism taking into account the following factors for each mode: (i) the direction of the transition moment, (ii) the extent of nitrogen lone pair and aromatic π-electron participation, and (iii) the direct field effect of the ortho substituent.

Many authors have shown that the stretching frequencies, the absorption intensities, and in some cases the band widths arising from vibrations localized in functional groups attached to an aromatic ring can be related to the electronic nature of the ring substituents through the HAMMETT substituent constants (o) 1 based on chemical reactivitv studies.Such correlations have been published for the OH stretching vibration in phenols 2 , the C=N stretching vibration in benzonitriles 3 ~5, the -NH stretching vibration in N-methvl anilines 6 , the NH2 stretching vibrations in anilines [5][6][7][8] , and the C = 0 stretching vibration in benzaldehvdes 9 , ethyl benzoates 9 and acetophenones 9 -10 .BROWN 11 has shown that in some cases such correlations are more appropriately made in terms of the electrophilic substituent constants o" 12 .The high precision and accuracy of the recent infrared measurements in this field has justified a statistical treatment of the data by RAO and VENKATARAGHAVAN 13 .

Mixtures of chlorobenzene and chlorobenzene-2-2H have been subjected to partial amination by sodamide in liquid ammonia and both the unreacted starting material and the product aniline have been analyzed for deuterium. Deuterium in the aniline is distributed approximately equally between the ortho and meta positions. The results give strong support to the mechanism proposed by Roberts and co-workers in which the slow step is the formation of an intermediate, such as benzyne, which is symmetrical with respect to carbon atoms 1 and 2.