Amines

Question 1

What is an amine?

Answer 1

An amine is an organic molecule derived from ammonia (NH₃) where one or more of the ammonia hydrogens has been replaced by a carbon chain.

To name an amine, remove the -e from the name of the parent alkane and replace it with -amine.

Question 2

When is “amino-“ used as a prefix to name amines?

Answer 2

The prefix amino- is used to name an NH₂ group as a substituent when there are higher priority groups in the molecule such as alcohols or carboxylic acids.

Amino- is also used as a prefix when an NH2 group is on a carbon that is not the first or last carbon of the chain.

Question 3

What is the name of this molecule?

Answer 3

butanamine.

To name an amine where the NH₂ group is on a terminal carbon, replace the -e of the parent alkane name with -amine.

Question 4

What is the name of this molecule?

Answer 4

2-aminopropanol.

The highest priority group on the carbon chain is the OH. Therefore, the molecule should be named as an alcohol with -ol replacing the -e of the parent alkane name. The NH₂ group is named as a substituent on the chain with the prefix amino-.

Question 5

When does the nitrogen of an amine have chirality?

Answer 5

An amine nitrogen has chirality if it has three or four asymmetric groups bound.

Tertiary amines invert spontaneously at room temperature and thus exist as a racemic mixture. Quaternary amines do not invert and thus maintain their chirality.

Question 6

It the following molecule chiral? Will a solution of this molecule at room temperature be optically active?

Answer 6

The molecule is chiral, but the solution will not be optically active.

The molecule is a tertiary amine with three different groups bound, so it is chiral. Tertiary amines spontaneously invert at room temperature, so a solution of this molecule is racemic and not optically active.

Question 7

What key chemical property of amines impacts physical properties such as boiling point and melting point?

Answer 7

Amines can form hydrogen bonds.

Hydrogen bonding in amines increases the boiling points and melting points of amines relative to alkanes with similar carbon chains.

Question 8

How do the boiling points of amines compare to those of alcohols with similar chain lengths?

Answer 8

The boiling points of amines are lower than those of analogous alcohols because alcohols have greater intermolecular forces due to stronger hydrogen bonding.

Question 9

How do the melting points of amines compare to those of alkanes with similar chain lengths?

Answer 9

The melting points of amines are higher than those of analogous alkanes because amines have greater intermolecular forces with hydrogen bonding.

Question 10

What type of reaction is an amide formation?

Answer 10

An amide formation is a nucleophilic substitution reaction where an amine attacks a carbonyl carbon and displaces a good leaving group.

Amines can attack the carbonyl carbon of acid chlorides and displace chlorine (a good leaving group) to form an amide.

Question 11

What product will this reaction form?

Answer 11

amide.

This is a nucleophilic substitution where the secondary amine attacks the carbonyl carbon and displaces the chloride (a good leaving group).

Question 12

How do amines react with nitrous acid?

Answer 12

Amines attack the nitrogen of nitrous acid and eventually form a diazonium compound (with the amine nitrogen and the nitrous acid nitrogen triple bonded to each other).

The diazonium group is an excellent leaving group.

Question 13

What product will this reaction form?

Answer 13

benzenediazonium cation.

The amine on the benzene ring attacks the nitrous acid oxygen and forms a diazonium cation.

Question 14

What type of reaction is an amine acylation?

Answer 14

In an amine acylation, an acyl group (RCO) is added to an amine, creating an amide.

The reaction is similar to amide formation.

Question 15

What product will this reaction form?

Answer 15

amide.

This is an acylation reaction where the amine nucelophilically attacks the acid chloride and displaces the chloride.

Question 16

What type of reaction is an amine alkylation?

Answer 16

In an amine alkylation, and alkyl group (R) is added to an amine.

Typically, an amine will perform a nucleophilic substitution on an alkyl halide. Alkylations can occur multiple times.

Question 17

How does an amine alkylation affect the nucleophilicity of the product?

Answer 17

Amine alkylation increases the product nucleophilictity because alkyl groups are electron donating.

Question 18

Why do exhaustive alkylations of amines by alkyl halides readily occur?

Answer 18

Since alkylations increase the nucleophilicity of the amine, the amine will continue to perform nucleophilic attacks on the alkyl halides until the amine is exhaustively alkylated.

Question 19

What product(s) will this reaction form?

Answer 19

triethylamine, diethylamine, and ethylamine.

The reaction forms multiple products because multiple alkylations occur. Alkylations increase the nucleophilicity of the amine which results in further alkylations.

Question 20

What type of reaction is a Hofmann Elimination?

Answer 20

In a Hoffman Elimination, a non-terminal amine is exhaustively methylated. The exhaustively methylated amine acts as a leaving group in an elimination that forms a double bond.

Question 21

How do Hofmann and Zaitsev eliminations differ?

Answer 21

In a Hofmann elimination, the less substituted double bond is formed. In a Zaitsev elimination, the more substituted double bond is formed.

Question 22

What product will this reaction form?

Answer 22

propene (and trimethylamine).

The reaction is a Hofmann elimination. The amine is exhaustively methylated in the first step and eliminated, creating a double bond, in the second step.

Question 23

What acid/base properties does an amine have?

Answer 23

Amines are basic and readily gain protons.

Question 24

Are amines readily deprotonated in base? Why or why not?

Answer 24

No.

Amines are basic and are readily protonated. They are not readily deprotonated.

Question 25

What substituent properties affect the basicity of an amine?

Answer 25

The following substituent properties affect the basicity of an amine:

1) The electronic properties of the substituents on the amine
2) The solvability of a substituted and protonated amine
3) The steric hindrance of the substituents on the amine

Question 26

How does an alkyl substituent affect the basicity of an amine?

Answer 26

Alkyl substituents increase the basicity of amines because alkyl groups are electron donors and increase an amine’s ability to donate electrons/accept a proton.

Question 27

How does the solvation of a substituted and protonated amine affect amine basicity?

Answer 27

Increased solvation of the protonated amine increases the basicity.

Solvation disperses the positive charge of the protonated amine and increases the basicity. Fewer alkyl groups on amines result in better solvation because the nitrogen is freer to hydrogen bond with water.

Question 28

How does the bulkiness of a substituent on an amine affect basicity?

Answer 28

Bulky substituents on amines decrease basicity because steric hindrance makes the amine a poorer proton acceptor.

Question 29

What effect do amines have on the stability of adjacent carbocations and why?

Answer 29

Amines stabilize adjacent carbocations by donating the lone pair electrons on the nitrogen.

Question 30

What resonance structure of the following molecule explains how amines stabilize neighboring carbocations?

Answer 30

The following resonance structure depics the nitrogen donating its lone pair electrons to the carbocation and increasing carbocation stability.

Question 31

How are imines formed?

Answer 31

Imines are formed when an amine with at least two hydrogens bound nucleophilically attacks a carbonyl carbon in the presence of acid catalyst.

The carbonyl oxygen leaves as water and the attacking nitrogen forms a double bond with the carbonyl carbon.

Question 32

What product will this reaction form?

Answer 32

Imine (and water).

The primary amine attacks the carbonyl carbon and the carbonyl oxygen leaves as water. The nitrogen forms a double bond with the carbonyl carbon.

Question 33

***do you mean enamines? amides covered previously

Question 34

***do you mean enamines? amides covered previously