Answers and Explanations

DISCRETE PRACTICE QUESTIONS

1 . C

NH 3    and H 2 O   are Lewis   bases   because nitrogen    and oxygen  can donate  lone    pairs.  Ag+ is  a   Lewis

acid    because it  can accept  a   lone    pair    into    an  unoccupied  orbital.

2 . C
Remember, good nucleophiles tend to have lone pairs or π bonds and are negatively charged or
polarized. Alkoxide (OR–) and hydroxide (OH–) anions are strong nucleophiles. Alcohols (ROH) and
carboxylic acids (RCOOH) are weak nucleophiles. The alkyl group of an alkoxide anion donates
additional electron density, making it more reactive than the hydroxide ion. The carboxylic acid
contains more electron-withdrawing oxygen atoms than the alcohol, making it less nucleophilic.

3 . D
Good electrophiles are positively charged or polarized. is a tertiary carbocation; it has a
positive charge, which makes it very electrophilic. CH 3 Cl and CH 3 OH are both polarized; however,
the leaving groups differ between these two. Cl– is a weaker base than OH– (HCl is a stronger acid
than H 2 O). As such, Cl– will be more stable in solution than OH–, which increases the electrophilic
reactivity of CH 3 Cl above CH 3 OH. CH 3 OCH 3 has a much less stable leaving group, CH 3 O–, and is
therefore significantly less electrophilic.

4 . A
Good leaving groups are weak bases, which are the conjugates of strong acids. Leaving groups
must also be stable once they leave the molecule. H 2 O is, by far, the most stable leaving group
and will be extremely unreactive once it leaves the molecule through heterolysis. Br– is the
conjugate base of HBr; HO– is the conjugate base of water. HBr is a much stronger acid than
water, so Br– is a better leaving group than HO–. Finally, hydride (H–) is a very poor leaving group
because it is extremely unstable in solution.