A compound with molecular formula C₄H₅N has a strong absorption at 2250 cm[latex]^{−1}[/latex]. Suggest two possible structures and explain how they could be distinguished by other infrared absorptions.

The absorption is due to a nitrile group. There is an additional deficiency of two hydrogen atoms, which could be due to a double bond or a ring. The stretching frequency is at the upper value of the range for nitriles (2200–2250 cm[latex]^{−1}[/latex]). Thus, the double bond cannot be in conjugation with the nitrile group because such a resonance stabilized functional group would absorb at lower wavenumber. Only one unsaturated nitrile is possible, and only one cycloalkylnitrile is possible.

Question 21.59: A compound with molecular formula C₄H₅N has a strong absorpt......

Organic Chemistry Study Guide: Key Concepts, Problems, and Solutions [1424398]

A compound with molecular formula C₄H₅N has a strong absorption at 2250 cm $^{−1}$ . Suggest two possible structures and explain how they could be distinguished by other infrared absorptions.

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The absorption is due to a nitrile group. There is an additional deficiency of two hydrogen atoms, which could be due to a double bond or a ring. The stretching frequency is at the upper value of the range for nitriles (2200–2250 cm $^{−1}$ ). Thus, the double bond cannot be in conjugation with the nitrile group because such a resonance stabilized functional group would absorb at lower wavenumber. Only one unsaturated nitrile is possible, and only one cycloalkylnitrile is possible.