N-H stretch amides

Table 10.24 Amide N-H stretching vibrations (and other bands in same region) ...

The polyamides and polyureas exhibited broad, intense N-H stretches around 3300 cm- , a very strong carbonyl stretching vibration was present at 1630 cm- . The amide II band was evident near 1540 cm- . jn addition, sp C-H stretches occurred around 3100 cm- an(j asymmetric and symmetric sp3 c-H stretches at 2950 and 2860 cm- , respectively. The polyurethane showed the carbonyl absorption near 1700 cm-1 and C-0 stretches in the vicinity of... 

In 3, the amino functional group is two methylene units removed from the ferrocene nucleus. It appears from the instantaneous and quantitative formation of h from 3 that this feature minimizes steric effects and also enables 3 to undergo the Schotten-Baumann reaction readily without the classical a-metallocenylcarbenium ion effects providing any constraints. The IR spectrum of showed the characteristic N-H stretch at 3320 cm" (s), the amide 1 (carbonyl) stretch at 1625 an - -(s), the amide II (N—H) stretch at 1540 cm (s), and the amide III band at 1310 cm 1(m). In addition, characteristic absorptions of the ferrocenyl group were evident at 1100 and 1000 cm l (indicating an unsubstituted cyclopentadienyl ring) and at 800 cm"l. 

The broadband at 3270 cm-1 is due to the O-H stretching vibration of the hydroxyl group. Moreover, the N-H stretching vibration absorption for open-chain amides occurs near 3270 cm-1 in the niclosamide solid state. 

The chemical structures of these polymers were characterized using FT-IR. Poly(1,3-phenylene isophthalamide) (PMI) and poly (2,4-difluoro-l,5-phenylene isophthalamide) (2,4-DIF-PMI) shoved N-H stretching bands at 3400-3200 cm l and C==0 stretching bands(amide I) at 1630-1650 cm-. Poly(2,4-difluoro-1,3-phenylene trimellitic amide-imide) (2,4-DIF-PMTAI) showed additional bands at 1740 and 1796 cm l corresponding to imide C==0 stretching band at 1625 cif and C-0-C stretching bands at 1255 and 1050 cm l. 

When the presence of a carbonyl group (> 0 = 0) has been established further study will reveal whether the carbonyl group is aldehyde, ketonic, ester or samide etc. Aldehydes can be recognised by its characteristics C-H stretching, esters from its C-0 stretching and amides for N-H stretching. 

G 1610 cm C=C stretch Aromatic ring stretch, broad band possibly obscuring amide N-H bend... 

FIGURE 3.28. 2-methylpropanamide. A. The N—H stretch, coupled, primary amide, hydrogen bonded asymmetric, 3352 cm-1 symmetric, 3170 cm1. B. Aliphatic C—H stretch, 2960 cm-1. C. Overlap C=0 stretch, amide I band, 1640 cm-1 see Table 3.3. 

N—H Stretching Vibrations In dilute solution in nonpolar solvents, primary amides show two moderately intense NH stretching frequencies corresponding to the asymmetrical and symmetrical NH stretching vibrations. These bands occur near 3520 and 3400 cm-1, respectively. In the spectra of solid samples, these bands are observed near 3350 and 3180 cm-1 because of hydrogen bonding. 

In lactams of medium ring size, the amide group is forced into the s-cis conformation. Solid lactams absorb strongly near 3200 cm-1 because of the N—H stretching vibration. This band does not shift appreciably with dilution since the s-cis form remains associated at relatively low concentrations. 

Formation of an amide is also indicated in the reaction of PCTFE with Cr(CO)6 and the primary amine, benzylamine. The infrared absorption spectrum shows an N-H stretch centered at 3400 cm, aromatic C-H stretches at 3063 and 3030 cm1, aliphatic C-H stretches at 2933 and 2876 cm1, a broad amide I/amide II band ranging from 1680-1580 cm1, and a C-N stretch at 1454 cm1. The C-Cl stretch at 970 cm1 also shows a significant decrease in... 

A strong carbonyl absorption is evident in the spectra of all amides, although the frequency of absorption varies somewhat with the structure of the amide. Thus primary amides generally absorb near 1680 cm 1, whereas secondary and tertiary amides absorb at slightly lower frequencies. The N—H stretching frequencies of amides are closely similar to those of amines and show shifts of 100 cm-1 to 200 cm 1 to lower frequencies as the result of hydrogen bonding. Primary amides have two N—H bands of medium intensity near 3500 cm 1 and 3400 cm 1, whereas secondary amides, to a first approximation, have only one N—H band near 3440 cm 1. However, a closer look reveals that the number, position, and intensity of the N—H bands of mono-substituted amides depend on the conformation of the amide, which can be either cis or trans ... 

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