S. Pinchas

The infrared absorption spectrum of 18O-labelled nitrobenzene

The absorption spectrum of a sample which was composed of about 49 per cent C6H5N16O18O, 32 per cent C6H5N16O2 and 19 per cent C6H5N16O2 was measured, in solution in carbon disulphide or carbon tetrachloride or as a liquid, in the 3700–390 cm−1 region, in comparison to the corresponding spectrum of normal nitrobenzene. Only the bands at 2860, 1531, 1349, 850, 790, 702, 681, 532 and 417 cm−1 were observed to be affected by the 18O-labelling. The band at 850 cm−1 is re-assigned to an NO2 symmetric deformation while the 681 cm−1 band is assigned to an out-of-plane ring deformation. The band at 532 cm−1 is shown to be very sensitive to the mass of the oxygen atoms and is therefore due to a mode of vibration which has a strong NO (out-of-plane) bending character.

The infra-red absorption spectrum of 18O-labelled urea

Abstract The absorption spectra of normal and 87 atom % 18 O-urea in the 400-400 cm −1 region were measured and compared for Nujol mulls, fine powders and (partly for) solutions in a dimethylsulphoxide-carbon tetrachloride mixture. The assignment of the bands which were observed to undergo an isotopic shift is discussed. An intensity inversion of the bands in the CO stretching region, which occurs on going over from the solid state to solution, both for the normal and the labelled urea, is explained on basis of a difference in the character of the higher band in each case.

The C-O stretching frequency of hydrated isotopic phenolate ions

Abstract The C-O stretching i.r. absorption band of the C 6 H 5 - 18 O − ion in aqueous solution appears at 1259 ± 1 cm −1 as compared with the respective value of 1281 ± 2 cm −1 in the case of the C 6 H 5 - 16 O − ion.

The i.r. absorption of 86% 18O-potassium permanganate

Abstract The absorption of potassium bromide pellets of normal and labelled potassium permanganate was measured in the 4000-220 cm−1 region. The assignment of the v1, v2, v3 and v4 modes of the permanganate ions to the absorption bands observed at 844, 385, 910 and 407 cm−1, in the case of the normal salt, and at 806, 368, 873 and 386 cm−1, in the case of the heavy salt, is confirmed. The agreement between the observed frequency of the labelled permanganate absorption bands and that calculated theoretically is very good.

The infra-red absorption of 75% 18O-barium phosphate

Abstract The infra-red absorption of Nujol mulls of normal and 75 atom % 18 O-barium-phosphate was measured in the 3700-360 cm −1 region. The assignment of all the observed bands is discussed and confirmed on basis of the valence forces assumption. The agreement between the observed and calculated frequencies of the labelled sample bands is satisfactory.

The anomalous behaviour of 18O-labelled compounds—XVI[1]: The relative integrated intensity of the main 18O-sensitive Raman bands of monomeric 18O-labelled benzoic acid

Abstract The 20–3500 cm−1 Raman spectrum of a dilute CH2Cl2 solution of 92.9 atom% 18O-benzoic acid was compared with the corresponding spectrum of a similar solution of normal benzoic acid. The observed bands were assigned to their original modes of vibration. The relative integrated intensity of the 18O-sensitive bands of normal benzoic acid observed thus at 414, 790 and 1644 cm−1 was compared with the respective intensity of the corresponding 18O-benzoic acid bands at 400, 774 and 1628 cm−1. The latter intensity was found to be in each case 30–50% less than the former one.

The integrated absorption intensity of the CO stretching bands of normal and 15N-barbituric acid

Abstract The integrated absorption intensity of the CO stretching bands of 99 % 15N-barbituric acid dissolved in dimethylsulphoxide was measured in comparison with that of the CO bands of normal barbituric acid and was found to be practically the same in both cases. The origin of the different CO bands of barbituric acid is discussed on basis of the observed 15N-isotope shifts of these bands. The assignment of other bands observed for the solution of this acid is suggested.

The anomalous behaviour of 18O-labelled compounds—XIV Association of normal and 18O-labelled water in dioxan solutions

Abstract The mean molecular weight, mean number of associated molecules, association degrees and various association constants of normal and 18 O-labelled water in 0.1–2.3 molar solutions in dioxan were determined cryoscopically. It was thus found that the hydrogen bonding association of H 2 18 O in dioxan solutions is significantly weaker than that of normal water.

The infra-red absorption spectrum of 18O-labelled triphenylcarbinol

Abstract The absorption of normal and 78 at.% triphenylmethyl carbinol was measured in the region 216–4000 cm −1 in dilute solution in carbon tetrachloride. The bands observed in the range 216–700 cm −1 are assigned and previous assignment for the 700–3500 cm −1 bands is checked on the basis of the observed 18 O-isotopic shifts of these absorption bands. It is shown that the 1330 cm −1 band previously [2] assigned to the in-plane OH bending vibration really belongs to a CC stretching mode while this bending vibration is responsible for the absorption at 1298 cm −1 . The integrated absorption intensity of the monomeric 18 OH stretching band is about 41 per cent lower than that of the corresponding 16 OH band.

Splitting of the CC stretching vibration of 3-substituted cyclenes

Abstract Pure samples of 3-methylcyclobutene, 3-methylcyclopentene, 3-methylcyclohexene and 3-methylcycloheptene were synthesized and their infrared absorption spectra measured. While 3-methylcyclobutene shares the CC stretching band splitting of the 3-substituted cyclopentenes and cyclohexenes, 3-methylcycloheptene does not. This fact is ascribed to the flexibility of the cycloheptene ring.