Exam 2 - Acetal Formation, Cyclic Acetals, -OCH3 conversion

Question 1

You can use cyclic acetal formation as ___ ___ for ketones!

Answer 1

protecting groups

Question 2

A(n) ___ is when 2 OR groups are on the same C.

Answer 2

acetal

Question 3

Anomeric C = ___ next to a(n) ___.

Answer 3

C next to an O

Question 4

You can convert a cyclic acetal to a ketone by adding ___ and ___.

Answer 4

H2O and HCL

Question 5

___ ___ = C next to an O.

Answer 5

Anomeric C

Question 6

A ketone + double-sided alcohol + HCl can create a ___ ___.

Answer 6

cyclic acetal

Question 7

Acid-mediated acetal formation is thermodynamically ___. This is because it requires ___ molecules to become ___ molecules.

Answer 7

thermodynamically unfavorable, requires 3 molecules to become 2 molecules (Hemiacetal + ethanol + HCl -> Acetal + H2O)

Question 8

Cyclic acetal formation mechanism is ___! It has the same intermediates as forward direction.

Answer 8

reversible

Question 9

Sometimes, a chair conformation can be more stable with more groups axial, as long as the ___ cancel each other out.

Answer 9

dipoles

Question 10

You can change a -OCH3 group from equatorial to axial in a chair conformation, by adding ___ and ___. This will create the ___ ion intermediate in the mechanism.

Answer 10

OH3OH and HCl, oxonium ion

Question 11

Cyclic acetal formation is more thermodynamically favorable, as it only requires ___ molecules to become ___ molecules.

Answer 11

requires 2 molecules to become 2 molecules

Question 12

You ___ use base-mediated acetal formation, as ___ reaction will take place. You ___ make a good LG.

Answer 12

cannot, No reaction, Cannot make a good LG

Question 13

An acetal is when ___ groups are on the same ___.

Answer 13

2 OR groups on the same C

Question 14

___ acetal formation is more thermodynamically favorable.

Answer 14

Cyclic acetal formation

Question 15

In acid-mediated acetal formation, a hemiacetal can react with ___ and ___ in order to make an acetal.

Answer 15

ethanol and HCl (or pTsOH)

Question 16

You can use cyclic acetals as protecting groups for ketones! First, add your ___ and ___ in order to convert the ketone to a cyclic acetal. Then, your other groups are open for other reactions, such as ___/___ reactions. You can then convert the cyclic acetal back to a ketone by adding ___.

Answer 16

double-sided alcohol and HCl, Grignard/Organolithium reactions, H2O

Question 17

Two ways to push the acid-mediated acetal formation equilibrium towards product: (via Le Chatlier’s Principle)

Answer 17

1) Remove H2O 2) Excess Alcohol (Ethanol)