54P - Organic Chemistry (Mcmurry)

Question

The compound whose ¹H NMR spectrum is shown has the molecular

formula C₄H₇O₂CI and has an infrared absorption peak at 1740cm-1.

Propose a structure.

Step-by-Step Solution

Answer

Step 1: 1 H NMR spectroscopy

The proton NMR spectroscopy can be used to identify the structure of different molecules.  The different kinds of electronically non equivalent hydrogens can be identified from the ¹H NMR spectroscopy.

Step 2: Proposing the structure of the compound C 4 H 7 O 2 CI

The degree of unsaturation for the compound  can be given as: C₄H₇O₂CI

The compound has one degree of unsaturation. The possible structures of the compound are CH₃CH₂CO₂CI  and CICH₂CO₂CH₂CH₃  . The chemical shift can distinguish between them.

                           Structure of compounds A and B

In compound A, the protons are connected to the carbon bonded to both oxygen and chlorine (-OCH₂CI) are expected to absorb far downfield in the refion 5.0 to 6.0 ppm. Because no signal is present in this region of hydrogen NMR spectrum, The unknown will be B. the quartet absorbing at 4.26 $\partial$is typical of a CH₂ group next to the electronegative atom and coupled with a methyl group.