Final answer:
2,3-dimethyl-2-butene would not show a peak for a C=C stretch in an IR spectrum because its symmetrical structure makes the stretching vibrations of the double bonds infrared inactive.
Step-by-step explanation:
The molecule that would not show a peak in an IR spectrum characteristic of a C=C stretch among the provided options is 2,3-dimethyl-2-butene. This compound does not have a C=C bond because it is a symmetrical molecule, and according to molecular symmetry rules, symmetric molecules such as this one have stretching vibrations that are infrared inactive.
In infrared spectroscopy (IR), the absorption of light depends on changes in the dipole moment of the molecule, hence molecules with symmetrical double bonds, like 2,3-dimethyl-2-butene, do not typically show absorption for a C=C stretch. In contrast, the C=C stretch is identifiable in IR spectra for other alkenes like 1-butene, 2-chloro-3-methyl-2-butene, and 2-methyl-2-butene, as long as the double bonds are not in a symmetrical environment.