CHEM 1020 MIDTERM I EXAM QUESTIONS WITH
ACCURATE SOLUTIONS
What is formed when alcohols are added to aldehydes or ketones? -- Answer ✔✔
acetals and ketals
What conditions are required for acetal formation? -- Answer ✔✔ acidic conditions
What are the steps involved in acetal formation? -- Answer ✔✔ 1) alcohol takes a
proton from the acid and uses it to protonate the carbonyl
2) the alcohol attacks the carbonyl carbon
3) the alcohol is deprotonated and a hemiacetal is formed
4) the OH group is protonated to form water, which acts as the leaving group
5) pi donation occurs to kick off the leaving group and reform the carbonyl
6) the alcohol attacks the carbonyl carbon again
7) the nucleophile is deprotonated to form the acetal
What happens when amines are added to aldehydes or ketones? -- Answer ✔✔ only
one equivalent of the amine is incorporated into the structure, and the C=O bond is
replaced by a C=N bond, forming an imine
, What is the mechanism of imine formation? -- Answer ✔✔ 1) acid is used to protonate
the carbonyl oxygen (can also skip this step and just start at step 2 since an amine is a
good nucleophile)
2) the amine attacks the carbonyl carbon
3) the amino group is deprotonated to form a carbinolamine (a molecule with an amino
group and an OH group
4) the OH group is protonated to form water, which will act as LG
5) pi donation occurs to kick off the LG, forming a C=N bond with a positive charge on
the N (iminium ion)
6) the iminium ion is deprotonated to form the amine
What is the mechanism of enamine formation? -- Answer ✔✔ 1) an aldehyde or ketone
is attacked at the carbonyl carbon by a secondary amine
2) a proton is transferred from the amino group to the negatively charged oxygen to
form an OH group
3) the OH group is protonated to form water, which will act as LG
4) pi donation occurs to kick off the LG and replace the C=O bond with a C=N bond
with a positive charge on N
5) since the N is not protonated, must remove an H from a neighboring carbon to get
rid of the positive charge on N, and this shifts the double bond one position over to
form the enamine
When is a cyclic acetal formed? -- Answer ✔✔ when a diol is used as a nucleophile in an
acetal formation reaction, resulting in an intramolecular nucleophilic attack that cyclizes
the molecule
What is the mechanism of imine hydrolysis? -- Answer ✔✔ 1) the imine is protonated
ACCURATE SOLUTIONS
What is formed when alcohols are added to aldehydes or ketones? -- Answer ✔✔
acetals and ketals
What conditions are required for acetal formation? -- Answer ✔✔ acidic conditions
What are the steps involved in acetal formation? -- Answer ✔✔ 1) alcohol takes a
proton from the acid and uses it to protonate the carbonyl
2) the alcohol attacks the carbonyl carbon
3) the alcohol is deprotonated and a hemiacetal is formed
4) the OH group is protonated to form water, which acts as the leaving group
5) pi donation occurs to kick off the leaving group and reform the carbonyl
6) the alcohol attacks the carbonyl carbon again
7) the nucleophile is deprotonated to form the acetal
What happens when amines are added to aldehydes or ketones? -- Answer ✔✔ only
one equivalent of the amine is incorporated into the structure, and the C=O bond is
replaced by a C=N bond, forming an imine
, What is the mechanism of imine formation? -- Answer ✔✔ 1) acid is used to protonate
the carbonyl oxygen (can also skip this step and just start at step 2 since an amine is a
good nucleophile)
2) the amine attacks the carbonyl carbon
3) the amino group is deprotonated to form a carbinolamine (a molecule with an amino
group and an OH group
4) the OH group is protonated to form water, which will act as LG
5) pi donation occurs to kick off the LG, forming a C=N bond with a positive charge on
the N (iminium ion)
6) the iminium ion is deprotonated to form the amine
What is the mechanism of enamine formation? -- Answer ✔✔ 1) an aldehyde or ketone
is attacked at the carbonyl carbon by a secondary amine
2) a proton is transferred from the amino group to the negatively charged oxygen to
form an OH group
3) the OH group is protonated to form water, which will act as LG
4) pi donation occurs to kick off the LG and replace the C=O bond with a C=N bond
with a positive charge on N
5) since the N is not protonated, must remove an H from a neighboring carbon to get
rid of the positive charge on N, and this shifts the double bond one position over to
form the enamine
When is a cyclic acetal formed? -- Answer ✔✔ when a diol is used as a nucleophile in an
acetal formation reaction, resulting in an intramolecular nucleophilic attack that cyclizes
the molecule
What is the mechanism of imine hydrolysis? -- Answer ✔✔ 1) the imine is protonated
