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GENERAL INFORMATION ON NITRO COMPOUNDS 175

group near 280 mμ arises from the transition of free electrons surrounding oxygen

atoms to the π orbital.

INFRA-RED ABSORPTION SPECTRA

In the infra-red region the nitro group produces two bands of high intensity:

one near 6.4μ (1563 cm

-1

), which characterizes asymmetric vibrations of the

bonds of the nitro group (I), and another near 7.4μ (1351cm-1), which

characterizes symmetric vibrations of the bonds of the nitro group (II).

In addition to this, vibrations of the nitro group ranging from 4.0-4.17μ

(2500-2398 cm-1) exist (Kornblum, Ungnade and Smiley [19]), but they are of

little significance for identification according to the authors.

On the basis of their investigations of nearly 35 nitro compounds, Kornblum,

Ungnade and Smiley have distinguished the vibrations of primary, secondary and

tertiary nitro groups in aliphatic nitro compounds (Table 23).

TABLE 23

Nitro compounds asymmetric

Vibrations

I symmetric

primary

secondary

tertiary

μ cm

-1

μ cm

-1

6.45±0.01 1550±2 7.25±0.02 1379±3

6.45±0.01 1550±2 7.37 1357

6.51±0.01 1536±2 7.41±0.02 1348±3

It can be seen from these data that the position of the nitro group band depends
on whether the group is primary, secondary or tertiary.
The results of the above investigations are at the same time a summary of the
earlier data obtained by several authors: Barnes et al. [20], Smith et al. [21], Haszel-

dine [22] and Brown [23].

Bellamy [24] gives the figures:

1565-1545 cm-1 and 1383-1360 cm-1

for both primary and secondary nitroaliphatic compounds. In tertiary nitro com-

pounds the frequencies are lower:

1545-1530 cm-1 and 1358-1342 cm-1

Conjugation of the nitro group by attachment to an ethylenic double bond

leads to a fall in both frequencies, according to Shechter and Shepherd [25] and

Brown [23], to 1524-1515 cm-1 and 1353-1346 cm-1