Tertiary amines infrared spectra

Primary amines may be readily distinguished from secondary and tertiary analogues by the presence of two absorption bands in the infrared spectrum between 3320 and 3500 cm-1 (symmetric and antisymmetric NH str.). Secondary amines exhibit a single absorption band at about 3350 cm-1 (NH str.). In both cases deformation modes for the NH bond appear at about 1600 cm-1. There is no satisfactory absorption to allow a definitive characterisation in the case of tertiary amines. In the nuclear magnetic resonance spectrum of primary and secondary amines, the nitrogen-bound hydrogens are recognisable by their replaceability on the addition of deuterium oxide. 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

The reaction of III with two or four equivalents of n-butyllithium resulted in the formation of a new product, N, N-di-n-butyl-terf-butylamine (VI), in yields up to 16% of theory. This previously unknown tertiary amine was identified by infrared and mass spectrometric analyses. A comparison of the mass spectrum of VI with that of the known tri-n-butylamine (Table I) shows thait the same major peaks appear but in quite... 

These two vibrations are clearly visible at 3270 and 3380 cm in the infrared spectrum of butylamine, shown in Figure 22.1a. Secondary amines such as diethylamine, shown in Figure 22.1b, exhibit only one peak, which is due to N—H stretching, at 3280 cm Tertiary amines, of course, are transparent in this region, since they have no N—H bonds. 

This is not always the case because the peaks can merge into one broad peak due to hydrogen bonding, but two peaks are often observed. Because a secondary amine has only one N-H unit, it absorbs as a singlet (one peak) in this region. Tertiary amines do not have an N-H, and there is no absorption in this region. For the data presented in this and other chapters, a tertiary amine unit will not have N-H absorption in the infrared spectrum and its presence must be inferred from mass spectral data or from the empirical formula (see Sections 14.2.3 and 14.2.4). 

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