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5. Examine the IR below and classify the compound.
A. Alkane
B. Carboxylic acid
C. Alcohol
D. Alkene
♦ Relevant knowledge
Vibrational Spectroscopy
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Vibrational spectroscopy can also be referred to by the name of infrared spectroscopy (IR). In this kind of spectroscopy, a substance takes in IR radiation. The compounds that absorb IR radiations have a net null dipole moments. Functional groups absorb certain frequencies within the IR spectrum. The stretching between atoms is seen as C-H observed in the alkane (gives moderately high peaks). The bending between atoms can also be seen, but the peak are not as sharp.
In infrared spectrum (IR) Functional groups absorb at a specific wavenumber.
A) Alkane absorbs at a frequency of 300 – 2840 cm-1 because of carbon – hydrogen stretching. Alkanes are saturated substances.
B) Carbocylic acid is absorbed at a specific frequency of 1760 cm-1 because of carbonyl carbon inside carboxylic acid. -OH group of carboxylic acid absorbs at 3300-2500cm-1. It produces a strong and broad spectrum in the IR spectrum.
C) Alcohols are functional groups that contain the -OH group. It is absorbed by 3700-3200 cm-1.
D) Alkene are an aliphatic chain with a double bonds between two carbons. It is absorbed at 3100-3000 cm-1.
Answer: C. Alcohol