Q: Which of the following IR absorptions would NOT be expected in the spectrum of butyronitrile?

A broad absorption near $$3400\ \text{cm}^{-1}$$

Question 1

Which functional group is most clearly indicated by the strong absorption near $$2249\ 	ext{cm}^{-1} in $$the IR spectrum of butyronitrile ($$\mathrm{CH_3CH_2CH_2C \equiv N}$$)?

Accepted Answer

A nitrile group ($$\mathrm{C \equiv N})$$

Question 2

In the IR spectrum of butyronitrile, which region would you expect to find the $$\mathrm{C-H}$$ stretching vibrations for the alkyl chain?

Accepted Answer

$$2850-2960\ 	ext{cm}^{-1}$$

Question 3

Which of the following compounds would show a strong IR absorption near $$2249\ 	ext{cm}^{-1}$$ similar to butyronitrile?

Accepted Answer

Pentanenitrile ($$\mathrm{CH_3CH_2CH_2CH_2C \equiv N})$$

Question 4

If the IR spectrum of a compound shows a strong absorption at $$2249\ 	ext{cm}^{-1}$$ and no significant absorption near $$1700\ 	ext{cm}^{-1}$$, which functional group is most likely absent?

Accepted Answer

A carbonyl group ($$\mathrm{C=O})$$

Question 5

Which statement best explains why the $$\mathrm{C \equiv N}$$ stretch in butyronitrile appears at a higher wavenumber than the $$\mathrm{C=O}$$ stretch?

Accepted Answer

Triple bonds are stronger and stiffer than double bonds, resulting in higher vibrational frequencies.

Question 6

A student analyzes an unknown compound and observes a strong IR absorption at $$2249\ 	ext{cm}^{-1}$$ and several peaks between $$2850$$ and $$2960\ 	ext{cm}^{-1}. $$Which compound is most likely present?

Accepted Answer

Butyronitrile ($$\mathrm{CH_3CH_2CH_2C \equiv N})$$

Question 7

Which of the following IR absorptions would NOT be expected in the spectrum of butyronitrile?

Accepted Answer

A broad absorption near $$3400\ 	ext{cm}^{-1}$$

Question 8

If a compound's IR spectrum shows a strong, sharp absorption at $$2249\ 	ext{cm}^{-1}$$, what does this indicate about the bond type?

Accepted Answer

A triple bond between carbon and nitrogen

Question 9

Which region of the IR spectrum is known as the 'fingerprint region' and is useful for distinguishing between isomers?

Accepted Answer

$$600-1400\ 	ext{cm}^{-1}$$

Question 10

A chemist observes a strong IR absorption at $$2249\ 	ext{cm}^{-1}$$ and assigns it to a nitrile group. Which other functional group could potentially absorb in a similar region, possibly causing confusion?

Accepted Answer

An alkyne ($$\mathrm{C \equiv C})$$

Organic Chemistry Exam Study Guide: IR Spectroscopy, Reactions, and Nomenclature

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