Alcohols

Question 1

If no higher priority functional groups are present, what suffix will a hydroxyl (-OH) group give to the molecule name?

Answer 1

A hydroxyl, or alcohol, group gives the ending -ol.

Ex: Ethanol is an ethane chain, with one hydroxyl group in place of one hydrogen. Ethane-ol gives us ethanol.

Question 2

If no higher priority functional groups are present, what suffix will two hydroxyl (-OH) group give to the molecule name?

Answer 2

Two hydroxyl, or two alcohol, groups gives the ending -diol.

Ex: Methanediol is a methane molecule, with two hydroxyl groups in place of two hydrogens. Methane-diol gives us methanediol.

Question 3

How is an alcohol group represented in the name, if it is present in a molecule that also has higher priority functional groups?

Answer 3

An alcohol group is indicated as a hydroxyl group in the name.

Ex: 1-hydroxypropanone is a propane chain, with a carbonyl group on the center carbon (ketone) and a hydroxyl group in place of one hydrogen on the first carbon. 1-hydroxyl-propane-ketone gives us 1-hydroxypropanone.

Question 4

What general type of alcohol is a terminal hydroxyl (-OH) group on the end of a carbon chain called?

Answer 4

A terminal hydroxyl group is called a primary alcohol.

Ex: 1-propanol is a propane chain, with one hydroxyl group in place of one hydrogen at the end of the chain. This is a primary alcohol.

Question 5

What general type of alcohol is a non-terminal hydroxyl (-OH) group (in the middle of a carbon chain) called?

Answer 5

A non-terminal hydroxyl group is called a secondary alcohol.

Ex: 2-propanol is a propane chain, with one hydroxyl group in place of one hydrogen in the center of the chain. This is a secondary alcohol.

Question 6

What general type of alcohol is a hydroxyl (-OH) group at the intersection of three carbon chains called?

Answer 6

A hydroxyl group at the intersection of three carbon chains is called a tertiary alcohol.

Ex: 2-methylbutanol is a butane chain, with one hydroxyl group in place of one hydrogen at the #2 carbon of the chain, and a methyl replacing another hydrogen at that same carbon. This is a tertiary alcohol.

Question 7

What is the IUPAC name of the following molecule?
What type of alcohol is it?

Answer 7

The molecule is 1-propanol, a primary alcohol.

Question 8

What is the IUPAC name of the following molecule?
What type of alcohol is it?

Answer 8

The molecule is 2-butanol, a secondary alcohol.

Question 9

What is the IUPAC name of the following molecule?
What type of alcohol is it?

Answer 9

The molecule is 1,3-butanediol, and contains both primany and secondary alcohol groups. Generally, these are termed diols.

Question 10

What is the IUPAC name of the following molecule?
What type of alcohol is it?

Answer 10

The molecule is 2-methylbutanol, and contains a tertiary alcohol groups.

Question 11

What type of intermolecular forces will alcohols exert on each other?

Answer 11

Alcohols will undergo hydrogen bonding.

Recall: any molecule that contains a F, N, or O attached to a hydrogen will hydrogen bond.

Question 12

How does the boiling point of an alcohol compare to an alkane of similar size?

Answer 12

The alcohol will have a higher boiling point.

Alcohols undergo hydrogen bonding, while alkanes undergo only London dispersion forces. If sizes are similar, intermolecular attractive forces determine the relative boiling point difference between two molecules.

Question 13

How does the boiling point of an alcohol compare to an aldehyde of similar size?

Answer 13

The alcohol will have a higher boiling point.

Alcohols undergo hydrogen bonding, while aldehydes undergo onle dipole-dipole interactions. If sizes are similar, intermolecular attractive forces determine the relative boiling point difference between two molecules.

Question 14

How does the boiling point of methanol compare to that of water?

Answer 14

Water has a higher boiling point than methanol.

Both water and methanol can undergo hydrogen bonding. However, each water molecule has two hydrogens bound to the oxygen, thus it can undergo twice as many hydrogen bonds per molecule, increasing the intermolecular attractive force and the boiling point.

The BP of water is 100°C, that of methanol is 65°C.

Question 15

How does branching of the carbon chain affect boiling point of an alcohol? (assuming all other factors remain constant)

Answer 15

Increased branching decreases boiling point of an alcohol.

Branching decreases the boiling point in general, not just for alcohols. The added branches increase possibility for resonance, induction, and overall lessening of polarity.

Question 16

Rank the following in order from lowest to highest boiling points.

Answer 16

Lowest to highest: tert-butyl alcohol (83C), isobutanol (108C), n-butanol (118C).

Branching decreases the boiling point due to an increased possibility for resonance, induction, and overall lessening of polarity. The highly branched tert-butyl alcohol has a b.p. difference of 35C from the unbranched n-butanol.

Question 17

Rank the following in order from lowest to highest boiling points.

Answer 17

Lowest to highest: 2,3-dimethyl-2-butanol (119), 3-methyl-2-pentanol (134), 1-hexanol (158C).

Branching decreases the boiling point due to an increased possibility for resonance, induction, and overall lessening of polarity. The highly branched 2,3-dimethyl-2-butanol has a b.p. difference of 39C from the unbranched 1-hexanol.

Question 18

How does branching of the carbon chain affect melting point of an alcohol? (assuming all other factors remain constant)

Answer 18

Between already branched alcohols, increased branching tends to increase melting point of an alcohol, as long as the branching creates a more compact structure.

Branching increases the melting point in general, not just for alcohols. The added branches makes the shape more compact and easier to stack into a solid.

The straight chain alcohol is not included in this comparison, since straight chains have no branching.

Question 19

Rank the following in order from lowest to highest melting points.

Answer 19

Lowest to highest: isobutanol (-102C), tert-butyl alcohol (25C).

Branching increases the melting point in general, as the added branches makes the shape more compact and easier to stack into a solid. Straight chain molecules (unbranched) are not included in this general rule.

Question 20

Rank the following in order from lowest to highest melting points.

Answer 20

Lowest to highest: 3-methyl-2-pentanol (-90C), 2,3-dimethyl-2-butanol (-14C).

Branching increases the melting point in general, as the added branches makes the shape more compact and easier to stack into a solid. Straight chain molecules (unbranched) are not included in this general rule.

Question 21

What is the result of putting an alcohol in an acidic environment?

Answer 21

The alcohol group is protonated.

Acidic environments will add an additional proton to the oxygen in the alcohol, turning the -OH group into an -OH₂⁺ group. The protonated alcohol group is an effective leaving group, hence protonation is the first step in many reactions involving alcohols.

Question 22

What is the product of the reaction of a primary alcohol with a nucleophile in an acidic environment?

Answer 22

A primary substituted product.

The acidic environment protonates the -OH group, turning it into an -OH₂⁺ group, which is an effective leaving group. The electrophylic carbon bound to this group is attacked by the nucleophile, and the -OH₂⁺is displaced via an S_N2 reaction mechanism.

Question 23

What is the product of the reaction of 1-propanol with HBr in an aqueous environment?

Answer 23

The product is 1-bromopropane.

This reaction occurs via an S_N2 mechanism, due to the primary nature of the carbon that the leaving group is bound to.

Question 24

What is the rate law for the reaction of 1-propanol with HBr in an aqueous environment?

Answer 24

Rate = k_obs [C₃H₇OH] [HBr]

This is the rate of an S_N2 reaction, as this reaction will be.

Question 25

What is the product of the reaction of a tertiary alcohol with a nucleophile in an acidic environment?

Answer 25

A tertiary substituted product.

The acidic environment protonates the -OH group, turning it into an -OH₂⁺ group, which is an effective leaving group. Since the leaving group is bound to a tertiary carbon, it leaves spontaneously via an S_N1 reaction. This generates a carbocation, which is later attacked by the nucleophile, forming a tertiary substituted product.

Question 26

What is the product of the reaction of tert-butanol with HBr in an aqueous environment?

Answer 26

The product is 2-bromo-tert-butane.

This reaction occurs via an S_N1 mechanism, due to the tertiary nature of the carbon that the leaving group is bound to.

Question 27

What is the rate law for the reaction of tert-butanol with HBr in an aqueous environment?

Answer 27

Rate = k_obs [C₄H₉OH]

This is the rate of an S_N1 reaction, as this reaction will be.

Question 28

In an oxidation reaction, what product(s) can a primary alcohol form?

Answer 28

Aldehyde, or carboxylic acid.

Weak oxidizing agents like PCC will stop at the aldehyde; strong oxidizing agents like dichromate will go to completion with the carboxylic acid.

Question 29

In an oxidation reaction, what product(s) can a secondary alcohol form?

Answer 29

Ketone.

Since there are two bonds from the central carbon already used, even a very strong oxidizing agent will have to stop and the ketone. A carboxylic acid group is not possible.

Question 30

In an oxidation reaction, what product(s) can a tertiary alcohol form?

Answer 30

None, other than the initial tertiary alcohol itself.

Since there are three bonds from the central carbon already used, even a very strong oxidizing agent will not add any new bonds to oxygen.

Question 31

What rearrangement is possible with a 1,2-diol under acidic conditions?

Answer 31

The Pinacol Rearrangement.

In a Pinacol Rearrangement, the -OH group which will yield a more stable carbocation (tertiary, or secondary) is protonated and leaves, and one of the alkyl chains rearranges to take its place. This allows the remaining -OH group to double bond to carbon (creating a carbonyl) and lose its proton to solution.

Question 32

What final product will 2,3-methyl-butan-2,3-diol make, when placed in an acid environment?

Answer 32

3,3-methyl-butan-2-one.

This reaction procedes via a Pinacol Rearrangement, since the original molecule is a diol on adjacent carbons. The final product shows that one of the methyl groups has shifted to replace the protonaded hydroxyl group that left. The remaining original hydroxyl has been converted to a ketone.

Question 33

What steps must be taken, in order for the final product of a multi-step chemical reaction to retain a highly attackable or reactive group?

Answer 33

A protecting group (protective group) must be added to modify the reactive functional group. This protecting group will then be removed in a final work-up step.

Ex: LAH will react carbonyls into alcohols. It’s possible that reduction of an ester is required, but the carbonyl has to be protected. If the carbonyl is first converted into an acetal (protecting group), then it will not react with LAH. The acetal can then be removed (deprotection) later by reacting with aqueous acid.

Question 34

What reactions have taken place if: during a multi-step reaction alcohol groups are converted to acetyl or benzoyl groups, and then using an acid or base work-up the original alcohol group is recovered?

Answer 34

Protection and deprotection.

Protection is the original conversion of the alcohol into either acetyl or benzoyl, creating a more stable and less reactive group.

Deprotection is the final work-up to produce the original alcohol group again.

Question 35

What product(s) will thionyl chloride (SOCl₂) create when reacted with an alcohol?

Answer 35

An alkyl-halide (specifically, an alkyl-chloride), where the alcohol -OH group is replaced with -Cl. HCl and SO₂ are also side products.

Question 36

What final product(s) will be formed in the reaction below?

Answer 36

Ethyl-chloride is the important product. HCl and SO₂ are also formed as side products.

An alcohol reacted with thionyl chloride will replace the -OH group with -Cl, and create HCl and SO₂ as side products.

Question 37

What product(s) will phosporus tribromide (PBr₃) create when reacted with an alcohol?

Answer 37

An alkyl-halide (specifically, an alkyl-bromide), where the alcohol -OH group is replaced with -Br. HBr and HP(O)(OH)₂ are also side products.

Note: Three alcohol molecules are necessary to fully react with one PBr₃ molecule.

Question 38

What final product(s) will be formed in the reaction below, assuming an excess of alcohol?

Answer 38

Ethyl-bromide (x3) is the important product. HP(O)(OH)₂ is also formed as a side product.

An alcohol reacted with phosphorus bromide will replace the -OH group on three alcohol molecules with -Br, and create HP(O)(OH)₂ as a side product.

Question 39

What advantage may be gained by reacting an alcohol with thionyl chloride (SOCl₂) or phosporus tribromide (PBr₃)?

Answer 39

The resulting alkyl-halide is very reactive, since a large halide (Cl, Br, or I) makes an excellent leaving group for nucleophilic substitution reactions.

This step can be a useful initial step to create a lower activation energy for subsequent steps in a multi-step reaction.

Question 40

What product(s) will methanesulfonyl chloride (CH₃SClO₂) create when reacted with an alcohol, in the presence of a base?

Answer 40

A mesylate ester, where the alcohol -OH group is replaced with -CH₃SO₂. The Cl^- ion and the conjugate acid of the base used, are also side products.

Question 41

What final product(s) will be formed in the reaction below, assuming this is run in a base (such as tryethylamine)?

Answer 41

Ethyl-mesylate is the important product. Cl^- and the conjugate acid of the base used are also formed as side products.

An alcohol reacted with methanesulfonate produces a mesylate ester, where the alcohol -OH group is replaced with -CH₃SO₂. The Cl^- ion and the conjugate acid of the base used, are also side products.

Question 42

What product(s) will toluenesulfonyl chloride (CH₃C₆H₄SClO₂) create when reacted with an alcohol?

Answer 42

A tosylate ester, where the alcohol -OH group is replaced with -CH₃C₆H₄SO₂. HCl is also a side product.

Question 43

What final product(s) will be formed in the reaction below, assuming this is run in a base (such as tryethylamine)?

Answer 43

Ethyl-tosylate is the important product. HCl is also formed as a side product.

An alcohol reacted with toluenesulfonyl chloride produces a tosylate ester, where the alcohol -OH group is replaced with -CH₃C₆H₄SO₂. HCl is also a side product.

Question 44

What advantage may be gained by reacting an alcohol with toluenesulfonyl chloride (CH₃C₆H₄SO₂Cl) or methanesulfonyl chloride (CH₃ClO₂S)?

Answer 44

The resulting tosylate or mesylate (respectively) is very reactive, since a large stable group makes an excellent leaving group for nucleophilic substitution reactions.

This step can be a useful initial step to create a lower activation energy for subsequent steps in a multi-step reaction.

Question 45

What is the process for the classic esterification synthesis reaction, known as the Fisher esterification?

Answer 45

In a Fischer esterification, an alcohol is reacted with a carboxylic acid in the presence of a dehydrating agent (and often a catalyst), to produce an ester and water.

This reaction is favored by using the alcohol in excess, a strong dehydrating agent (such as sulfuric acid), and/or by physically removing water (such as by distillation).

Question 46

What final product(s) will be formed in the reaction below, assuming this is run in an acid (such as sulfuric acid)?

Answer 46

Ethyl-ethanoate is the important product. Water is also formed as a side product.

An alcohol reacted with a carboxylic acid and a dehydrating agent (sulfuric acid) produces an ester and water as a side product. The alcohol -OH group attacks the backside of the carbonyl group, and the proton from the alcohol is transfered to the hydroxyl of the carboxylic, which leaves as water.

Question 47

What process(es) for esterification synthesis, are possible without a carboxylic acid substrate?

Answer 47

The two most common are alcoholysis of (1) acyl chlorides or (2) acid anhydrides.

(1) An alcohol is reacted with an acyl chloride (ideally in an anhydrous condition) producing an ester and HCl.
(2) An alcohol is reacted with an acid anhydride (ideally in an anhydrous condition) producing an ester and a carboxylic acid.

This reaction is favored by using anhydrous conditions, since acyl chlorides and acid anhydrides also react with water.

Question 48

What final product(s) will be formed in the reaction below, assuming this is run in an anhydrous environment?

Answer 48

Propyl-ethanoate is the important product. HCl is also formed as a side product.

An alcohol is reacted with an acyl chloride in an anhydrous environment will produce an ester and HCl.

Question 49

What final product(s) will be formed in the reaction below, assuming this is run in an anhydrous environment?

Answer 49

Propyl-propanoate is the important product. Propanoic acid is also formed as a side product.

An alcohol is reacted with an acid anhydride in an anhydrous condition to produce an ester and a carboxylic acid.

Question 50

What general term is used to describe the condensation of an acid and an alcohol?

Answer 50

Inorganic ester.

Ester is a general term for the condensation of an acid and an alcohol. An inorganic ester is simply an oxo compound where the double-bonded oxygen is on a heteroatom such as phosphorus, sulfur, or nitrogen.

Question 51

What type of molecule is this?

Answer 51

An inorganic ester, specifically a phosphoric acid ester.

Ester is a general term for the condensation of an acid and an alcohol. An inorganic ester is simply an oxo compound where the double-bonded oxygen is on a heteroatom such as phosphorus, sulfur, or nitrogen.

Question 52

What final product(s) will be formed in the reaction below, assuming an excess of phenol?

Answer 52

Triphenyl phosphate ester, and water as a side product.

Ester is a general term for the condensation of an acid and an alcohol. The -OH groups on phosphoric acid are protonated by the attacking alcohol and leave as water. This repeats for each of the three -OH groups, until three phenyl groups have been added in an inorganic ester formation.

Question 53

How does the acidity of the proton on an alcohol compare to the protons on other oxygen containing compounds (such as ketones, esters, COOH groups)?

Answer 53

The general ranking of acidity (assuming similar size/structure/induction) is, from least to most acidic: esters, aldehydes/ketones, alcohols, carboxylic acids.

For the ester/aldehyde/ketone acidity is assumed to be based on the alpha hydrogen, since there is no -OH group present.

Question 54

Rank the following (A,B,C) in order of least to most acidic.

Answer 54

Least to most acidic: C, B, A.

The general ranking of acidity (assuming similar size/structure/induction) is, from least to most acidic: esters, aldehydes/ketones, alcohols, carboxylic acids.