DAT Question of the Day

Correct Answer: B. E2

E2 is the likely reaction to occur here:

1. Consider the leaving group: if primary, the reaction will almost certainly be SN2. If tertiary, the reaction cannot be SN2. Depending on the type of nucleophile/base, it will either proceed with concerted elimination (E2) or through carbocation formation (SN1/E1).

2. Charged nucleophiles/bases (such as –OCH3 in this example) will favor SN2/E2 pathways (i.e. eliminate SN1/E1). If a charged species is not present, the reaction is likely to be SN1/E1.

3. Polar protic solvents (like CH3OH) tend to favor elimination (E2) over substitution (SN2). Polar aprotic solvents tend to favor substitution (SN2) relative to elimination (E2).

First, determine the lowest energy chair conformation required for reaction, where the LG is axial and any other large groups remain equatorial. Once determined, two pathways must be considered. Removal of the proton that provides the more stable (tri-substituted vs. di-substituted) double bond (recall Zaitsev’s rule) is the preferred pathway.

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Correct Answer: A. I

Of the possibilities, all have the molecular formula C8H12O, but only compounds I and III can have 5 chemically unique proton signals in the H NMR spectrum. The broad IR peak at 3400 (indicative of alcohol), and sharp peak at 3300 (alkyne C-H stretch) confirms the compounds identity as I.

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Correct Answer: C. The polarity of a molecule is dependent on its 3-D structure

A molecule’s dipole is an electric dipole with an inherent electric field (not be confused with a magnetic dipole which generates a magnetic field). Molecules can have dipole moments due to non-uniform distributions of positive and negative charges on the various atoms. For diatomic molecules there is only one (single or multiple) bond so the bond dipole moment is the molecular dipole moment, with typical values in the range of 0 to 11 D. For polyatomic molecules there is more than one bond, and the total molecular dipole moment may be approximated as the vector sum of all individual bond dipole moments.

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