Question

Deduce a possible structure for the compound with the IR absorptions below.

C₃H₅N: 3000, 2250 cm^-1

Answer 1

Analysing the given IR absorptions:

Frequency (in cm^-1)	(probable group)
2250 (strong)	CN
3000	sp3 CH stretching vibration ,(for absorption above 3000 unsaturation or sp2 CH may be present)

Index of hydrogen deficiency or degree of unsaturation (DoU) may be used to acertain the number of unsaturation:

DoU#C- #H/2 +#N/2 - #X/2 +1

Xhalogen atoms

#Cmeans number of carbon,#H is number of hydrogen and #N is number of nitrogen

For C3H5N,

DoU3-5/2 +1/2+12 (two unsaturation could be a triple bond (CN) or two double bonds.

Structure of molecule:CH3CH2CN(propanenitrile)