MCAT Biology : Functional Groups and Properties

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Functional Groups And Properties

Shown above is the chemical structure for penicillin. Which of the arrows is pointing to an amide group?

Possible Answers:

B

A

C

D

Correct answer:

B

Explanation:

The correct answer is arrow B. An amide group is a carbonyl group with a nitrogen that is in the alpha position (directly attached to the carbonyl carbon). Penicillin has two different amide groups in its chemical structure, but only one has an arrow pointing to it in the diagram. Arrow B points to a primary secondary amide, bond to one hydrogen and two carbons. The other amide in the molecule is a tertiary amide, bond to three carbons and no hydrogens.

Penicillin_a

Example Question #2 : Functional Groups And Properties

Which of the following statements about amide bonds is NOT true?

Possible Answers:

Amide bonds are polar

A secondary amide has the following structure.

 Mcat_8

Amides are mildly acidic, with primary amides having a pKa of approximately fifteen

The nitrogen is  hybridized, while the carbon and oxygen are  hybridized

Amides are formed by the combination of a carboxylic acid and an amine, resulting in the loss of water

Correct answer:

The nitrogen is  hybridized, while the carbon and oxygen are  hybridized

Explanation:

Amides have a structure of a ketone group adjacent to an amine group.

In an amide bond, all of the atoms (the nitrogen, the carbonyl oxygen, and carbonyl carbon) are hybridized because of resonance; the lone pair on nitrogen can delocalize into the carbonyl pi bond. The amide bond is polar, mildly acidic, with a secondary amide having the structure shown. Finally, amides are often formed by a condensation reaction between a carboxylic acid and an amine, which produces water as a byproduct.

Example Question #2 : Functional Groups And Properties

Drain cleaners are a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.

A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:

Pic_1

Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:

Pic_2

The NH4 molecule produced in Reaction 2 must have __________.

Possible Answers:

a positive charge due to the presence of an extra hydrogen

a negative charge, since one was also created on the other product

no charge, since N has a lone pair of electrons available to bond

an expanded octet for the N atom

a basic nature due to the presence of the nitrogen atom

Correct answer:

a positive charge due to the presence of an extra hydrogen

Explanation:

The additional H present on ammonia (NH3) requires the generation of the a positive charge on the molecule. This also must be created to balance the negative charge created on the associated anion product.

Example Question #3 : Functional Groups And Properties

Which of the following amines is the strongest base?

Possible Answers:

Ammonia

A secondary amine with electron-donating functional groups

A secondary amine with electron-withdrawing functional groups

A primary amine with an electron-donating functional group

Correct answer:

A secondary amine with electron-donating functional groups

Explanation:

Amines act as bases due to the lone pair on the nitrogen. Amine basicity can be increased or decreased by functional groups attached to the nitrogen. Electron-withdrawing groups decrease the basicity of an amine by lessening the effect of the lone pair, while electron-donating groups increase basicity by amplifying the lone pair effect. As a result, a secondary amine with an electron-donating functional groups will be the most basic amine.

Example Question #4 : Functional Groups And Properties

Ephedrine (shown below) contains what type of amine?

Mcat_problem_set_1

Possible Answers:

Neutral

Quaternary

Primary

Secondary

Tertiary

Correct answer:

Secondary

Explanation:

A secondary amine is an amine (nitrogen atom) that is attached to two carbon-containing groups (alkyl groups or aryl groups). The nitrogen in ephedrine is attached to two alkyl groups, making it a secondary amine.

Primary amines are generally written as . Secondary amines are generally written as . A tertiary amine will be bound to three different R-groups. Quaternary amines require a positive charge on the nitrogen atom to accommodate a fourth R-group.

Example Question #6 : Functional Groups And Properties

Your lab isolates a compound with the formula . Upon further analysis, you determine that the base structure is a benzene ring with a single constituent. Which of the following could be the identity of the compound?

Possible Answers:

None of these

Benzylmethylamine

Benzylamine

Benzylamide

Nitrobenzene

Correct answer:

Benzylamine

Explanation:

Nitro groups and amide groups both contain oxygen components, and cannot be found in the compound described. We also know that the benzene ring only has a single constituent, meaning that it cannot be a methylamine. The compound must be benzylamine, a benzene ring with a -CH2NH2 substituent.

Example Question #7 : Functional Groups And Properties

What is the name of the functional group that contains a vinylic hydroxyl group?

Possible Answers:

Aldehyde

Carboxyl

Enol

Keto

Correct answer:

Enol

Explanation:

Enol functional groups contain a hydroxyl group bonded to a carbon involved in a double bond with another carbon (vinyl carbon). An enol will usually undergo tautomerization to become a more stable keto.

Example Question #8 : Functional Groups And Properties

Ephedrine, whose structure is shown below, is used commonly as a stimulant and decongestant.

Mcat_problem_set_1

Ephedrine contains all of the following functional groups except __________.

Possible Answers:

amine

ketone

alcohol

N-methyl group

arene

Correct answer:

ketone

Explanation:

Ephedrine contains an arene (the aromatic benzene ring), an alcohol (the -OH group), an amine (the nitrogen-based group), and an N-methyl group (-CH3 attached to nitrogen). It does not contain a ketone (C=O), or any other carboxyl groups.

Example Question #2 : Mechanisms And Intermediates

Which of the following compounds would you expect to undergo a nucleophilic addition reaction?

Possible Answers:

Methyl ethanoate

Acetic acid

Propanal

Ethanamide

Correct answer:

Propanal

Explanation:

When dealing with carbonyl compounds, remember that a carboxylic acid and all of its derivatives will undergo nucleophilic substitution. Aldehydes and ketones will undergo nucleophilic addition. Propanal is a three-carbon aldehyde, and will thus undergo nucleophilic addition.

Acetic acid is a carboxylic acid, methyl ethanoate is an ether, and ethanamide is an amide; each of these would undergo nucleophilic substitution.

Example Question #9 : Functional Groups And Properties

Compound A, shown below, contains an example of what type of functional group?

Mcat_2

Possible Answers:

Ether

Ester

Carboxylic acid

Ketone

Nitrile

Correct answer:

Ester

Explanation:

Esters have the general molecular formula of , where  and  are carbon groups. The rightmost region of compound A shows an ester.

Ketones have the formula of , with a carbon-oxygen double bond. Ethers have the formula of , with an oxygen linked by single bonds within a carbon chain. An ester resembles adjacent ketone and ether groups. Carboxylic acids have the formula , resembling an ester with a hydrogen in place of a second carbon chain. Finally, the nitrile group has a formula of , with a triple bond between nitrogen and carbon.

Compound A also contains an aromatic function group (the benzene ring) and a nitro group, , on the far left side.

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