Chapter 15, Problem 15.30YT

Interpretation Introduction

Interpretation:

The stretching band in IR spectrum of the unknown compound in Figure 15-26 is to be labelled.

Concept introduction:

IR spectroscopy permits to distinguish different functional groups in the molecule. Each functional group possesses a particular type of vibration within a characteristic range of frequency. The longest wavelength absorption in the UV-vis spectrum has around 190 nm.

From the IR spectrum, the structure of the molecule is determined by the IHD of the molecular formula. This corresponds to a variety of combinations of double bonds, triple bonds, and rings. By consulting characteristic frequencies of absorption in IR spectroscopy table, we can determine the type of bond and appearance of the band on the spectrum.

The C-H stretch on the terminal alkyne tends to appear as a strong, narrow band in the ${\text{3260-3330 cm}}^{\text{-1}}$ region while the triple bond shows a weak peak at ${\text{2100-2260 cm}}^{\text{-1}}$; N-H stretches appear, a small, sharp peak at $2100{\text{ cm}}^{\text{-1}}$.