Band intensity Barbiturates

In symmetrical molecules, the three bands are all of similar intensity. In asymmetrical molecules, the band at the highest frequency is often less intense than the other two, and this is particularly so when the molecule is substituted in position I. The sodium salts of the barbiturates have only two bands in this region, since the molecule is no longer symmetrical, and these occur at a lower frequency, between 1700 and 1650 cm In addition, a broad strongly absorbing band occurs between 1600 and 1550cm the free barbiturates show practically no absorption in this region. The sodium salts of the thiobarbiturates... 

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