---
title: "Functional Groups and Families"
book: "School Chemistry — Grades 1 to 12"
subject: chemistry
language: en
chapter: 33
exercises: 15
source: https://one-course.com/books/chemistry/1/en/chapter/33-functional-groups-and-families
license: CC-BY-NC-SA-4.0
credit: "One Chemistry Book, One Course (one-course.com)"
---

# Chapter 33 — Functional Groups and Families

Open a bottle of vinegar, a bottle of nail-varnish remover, a bag of pear drops, and walk past a fishmonger’s stall: four smells, sharp, sweet-solvent, fruity and fishy, and four different kinds of [molecule](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-molecule). Each owes its smell, and most of its chemistry, not to its carbon skeleton but to a small group of [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) attached to it: oxygen and hydrogen in one place, a nitrogen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) in another. Chemists sort [organic compounds](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-organic) by these groups.

**You already know.**

[Skeletal formulas](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas), the names of [alkanes](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-alkane) and [alkyl groups](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-alkane), [isomers](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-isomer) ([Chapter 32](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#ch-g11-organic-skeletons)). [Polar bonds](https://one-course.com/books/chemistry/1/en/chapter/30-electronegativity-polarity-and-intermolecular-forces#def-g11-polarity-and-cohesion-polar-bond) and [hydrogen bonds](https://one-course.com/books/chemistry/1/en/chapter/30-electronegativity-polarity-and-intermolecular-forces#def-g11-polarity-and-cohesion-hydrogen-bond) ([Chapter 30](https://one-course.com/books/chemistry/1/en/chapter/30-electronegativity-polarity-and-intermolecular-forces#ch-g11-polarity-and-cohesion)).

![Vinegar, a solvent, fruit: each smell comes from a different group of atoms on a carbon skeleton.](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/img-50eeb0e80dad.jpg)

*Vinegar, a [solvent](https://one-course.com/books/chemistry/1/en/chapter/9-solutions-and-solubility#def-g6-solutions-and-solubility-solute), fruit: each smell comes from a different group of [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) on a carbon skeleton.*

## 33.1 Functional groups

**Definition 33.1 (Functional group).**

A *functional group* is a group of [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom), other than the carbon and hydrogen [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) of the skeleton linked only by single bonds, that gives a [molecule](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-molecule) its characteristic reactions. The compounds that share a functional [group](https://one-course.com/books/chemistry/1/en/chapter/20-the-periodic-table-a-first-look#def-g9-periodic-table-first-look-period) form a family.

![The main functional groups, and the five built on a carbonyl group C=O, drawn in full. R and R' stand for carbon chains (alkyl groups) and X for a halogen atom (F, Cl, Br, I).](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-b463312ff79b.svg)

*The main [functional groups](#def-g11-functional-groups-functional-group), and the five built on a carbonyl group $\ce{C=O}$, drawn in full. R and R$'$ stand for carbon chains (alkyl groups) and X for a [halogen](https://one-course.com/books/chemistry/1/en/chapter/23-electron-shells-and-the-periodic-table#def-g10-electron-shells-family) [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) (F, Cl, Br, I).*

## 33.2 Alcohols and their class

**Definition 33.2 (Alcohol, class of an alcohol).**

An *alcohol* has a hydroxyl group $\ce{-OH}$ bonded to a carbon [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) that has only single bonds. The *class of an alcohol* is primary, secondary or tertiary according to whether the carbon [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) bearing the $\ce{-OH}$ is bonded to one, two or three other carbon [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom). (Methanol, $\ce{CH3OH}$, whose carbon is bonded to none, is counted with the primary alcohols.)

![Three isomers C4H10O, three classes of alcohol.](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-43e36aef9624.svg)

*Three [isomers](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-isomer) $\ce{C4H10O}$, three classes of [alcohol](#def-g11-functional-groups-alcohol).*

## 33.3 Aldehydes, ketones, acids and esters

**Definition 33.3 (Aldehyde, ketone).**

A carbonyl group is a $\ce{C=O}$ [double bond](https://one-course.com/books/chemistry/1/en/chapter/24-lewis-structures-and-the-shape-of-molecules#def-g10-lewis-and-shape-multiple-bond). If its carbon [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) is at the end of the chain (bonded to at least one hydrogen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom)), the compound is an *aldehyde*; if it is inside the chain (bonded to two carbon [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom)), the compound is a *ketone*.

**Definition 33.4 (Carboxylic acid, ester).**

A *carboxylic acid* has a carboxyl group $\ce{-COOH}$, a carbonyl and a hydroxyl on the same carbon [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom). An *ester* has the group $\ce{-COO-}$ between two carbon chains: it is related to an acid, whose $\ce{-OH}$ has been replaced by an $\ce{-O-}$R$'$ coming from an [alcohol](#def-g11-functional-groups-alcohol).

**Example 33.5 (Ethyl ethanoate).**

The [solvent](https://one-course.com/books/chemistry/1/en/chapter/9-solutions-and-solubility#def-g6-solutions-and-solubility-solute) ethyl ethanoate, $\ce{CH3-COO-CH2-CH3}$, smells of pear drops and nail-varnish remover. Its “acid part”, $\ce{CH3-CO}$, comes from ethanoic acid $\ce{CH3-COOH}$ and gives the second word of the name, *ethanoate*; its “[alcohol](#def-g11-functional-groups-alcohol) part”, $\ce{O-CH2-CH3}$, comes from ethanol $\ce{CH3-CH2-OH}$ and gives the first word, *ethyl*. A later chapter shows how an [ester](#def-g11-functional-groups-carboxylic-acid) is made from its acid and its [alcohol](#def-g11-functional-groups-alcohol).

![Naming an ester: the alcohol part gives an alkyl name (ethyl), the acid part an ending in -oate (ethanoate); the name is “ethyl ethanoate”.](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-1ab9823b3c3a.svg)

*Naming an [ester](#def-g11-functional-groups-carboxylic-acid): the [alcohol](#def-g11-functional-groups-alcohol) part gives an alkyl name (*ethyl*), the acid part an ending in *-oate* (*ethanoate*); the name is “ethyl ethanoate”.*

## 33.4 Amines, amides, halogenoalkanes and alkenes

**Definition 33.6 (Amine, amide).**

An *amine* has a nitrogen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) bonded to a carbon chain by a single bond, as in $\ce{-NH2}$. An *amide* has a nitrogen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) bonded to the carbon of a carbonyl group, as in $\ce{-CO-NH2}$.

**Definition 33.7 (Halogenoalkane, alkene).**

A *halogenoalkane* is an [alkane](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-alkane) in which one or more hydrogen [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) are replaced by [halogen](https://one-course.com/books/chemistry/1/en/chapter/23-electron-shells-and-the-periodic-table#def-g10-electron-shells-family) [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) (F, Cl, Br, I). An *alkene* has a carbon–carbon [double bond](https://one-course.com/books/chemistry/1/en/chapter/24-lewis-structures-and-the-shape-of-molecules#def-g10-lewis-and-shape-multiple-bond), $\ce{C=C}$.

**Remark 33.8 (Smells and groups).**

Many small [amines](#def-g11-functional-groups-amine) smell of rotten fish, and the smell of fish that is no longer fresh is largely due to them. Many small [esters](#def-g11-functional-groups-carboxylic-acid) smell of fruit. Small [carboxylic acids](#def-g11-functional-groups-carboxylic-acid) smell sharp, like vinegar; propanone, a [ketone](#def-g11-functional-groups-carbonyl), is the familiar [solvent](https://one-course.com/books/chemistry/1/en/chapter/9-solutions-and-solubility#def-g6-solutions-and-solubility-solute) smell of nail-varnish remover.

## 33.5 Naming

**Method 33.9 (Naming an organic compound with one functional group).**

1. Find the longest carbon chain that *contains* the carbon of the [functional group](#def-g11-functional-groups-functional-group) (or, for an [alcohol](#def-g11-functional-groups-alcohol) or an [amine](#def-g11-functional-groups-amine) , the carbon that bears it): it gives the root.
2. Number the chain from the end that gives the [functional group](#def-g11-functional-groups-functional-group) the lowest number.
3. Replace the *-e* of the [alkane](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-alkane) by the ending of the family, preceded by the position of the group if needed: propan-2-ol, butan-2-one. ( [Aldehydes](#def-g11-functional-groups-carbonyl) , acids and [amides](#def-g11-functional-groups-amine) have their group at carbon 1: no number.)
4. Add the alkyl substituents as prefixes, with their positions, as for [alkanes](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-alkane) ; a [halogen](https://one-course.com/books/chemistry/1/en/chapter/23-electron-shells-and-the-periodic-table#def-g10-electron-shells-family) is always a prefix (2-chloropropane).

**Example 33.10 (Four names).**

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-0956ec5bc58b.svg) is propan-2-ol (a secondary [alcohol](#def-g11-functional-groups-alcohol)); ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-976d9a298eb9.svg) is butan-2-one; ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-dd56a484ecab.svg) is butanoic acid; ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-b4a7fb2936e7.svg) is 3-methylbutanal.

![A perfumer’s bench: many of the bottles hold esters, alcohols, aldehydes and ketones.](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/img-c988fda640c8.jpg)

*A perfumer’s bench: many of the bottles hold [esters](#def-g11-functional-groups-carboxylic-acid), [alcohols](#def-g11-functional-groups-alcohol), [aldehydes](#def-g11-functional-groups-carbonyl) and [ketones](#def-g11-functional-groups-carbonyl).*

**Safety.**

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-dd70dd6a23ed.svg)

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-dd24cbda8fb7.svg)

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-8534e22fe83d.svg)

Propanone is highly flammable and irritating to the eyes; its vapour makes one drowsy. Pure ethanoic acid is flammable and causes severe burns of the skin and the eyes; vinegar is a dilute solution of it. Smells are never tested by sniffing a flask: the vapour is wafted gently towards the nose with the hand, and only when the teacher says so.

## 33.6 Exercises

**Exercise 33.1 ★.**

Name the [functional group](#def-g11-functional-groups-functional-group) and the family of each compound: $\ce{CH3-CH2-CH2-OH}$; $\ce{CH3-CO-CH2-CH3}$; $\ce{CH3-CH2-COOH}$; $\ce{CH3-COO-CH3}$; $\ce{CH3-CH2-NH2}$.

**Solution of Exercise 33.1.**

Hydroxyl, [alcohol](#def-g11-functional-groups-alcohol); carbonyl inside the chain, [ketone](#def-g11-functional-groups-carbonyl); carboxyl, [carboxylic acid](#def-g11-functional-groups-carboxylic-acid); [ester](#def-g11-functional-groups-carboxylic-acid) group, [ester](#def-g11-functional-groups-carboxylic-acid); amino group $\ce{-NH2}$, [amine](#def-g11-functional-groups-amine).

**Exercise 33.2 ★.**

Name: $\ce{CH3-OH}$; $\ce{CH3-CH2-CH2-OH}$; $\ce{HCOOH}$; $\ce{CH3-CH2-CHO}$; $\ce{CH3-CO-CH3}$.

**Solution of Exercise 33.2.**

Methanol; propan-1-ol; methanoic acid; propanal; propanone.

**Exercise 33.3 ★.**

To which family does each compound belong: butan-2-ol, pentanal, methyl propanoate, propanamide, 2-bromopropane, but-1-ene?

**Solution of Exercise 33.3.**

[Alcohol](#def-g11-functional-groups-alcohol); [aldehyde](#def-g11-functional-groups-carbonyl); [ester](#def-g11-functional-groups-carboxylic-acid); [amide](#def-g11-functional-groups-amine); [halogenoalkane](#def-g11-functional-groups-halogenoalkane); [alkene](#def-g11-functional-groups-halogenoalkane).

**Exercise 33.4 ★.**

Write the [semi-structural formulas](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) of propanal and of propanone. Which is the [aldehyde](#def-g11-functional-groups-carbonyl)? How do you tell?

**Solution of Exercise 33.4.**

Propanal $\ce{CH3-CH2-CHO}$, propanone $\ce{CH3-CO-CH3}$. Propanal is the [aldehyde](#def-g11-functional-groups-carbonyl): its $\ce{C=O}$ carbon is at the end of the chain, bonded to a hydrogen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom); in propanone it is between two carbon [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom).

**Exercise 33.5 ★.**

Give the class of propan-1-ol, propan-2-ol and 2-methylpropan-2-ol.

**Solution of Exercise 33.5.**

Primary (the carbon bearing $\ce{-OH}$ has one carbon neighbour); secondary (two); tertiary (three).

**Exercise 33.6 ★★.**

Draw the [skeletal formulas](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) of pentan-3-ol, 2-methylbutanoic acid, hexan-2-one and propyl ethanoate.

**Solution of Exercise 33.6.**

Pentan-3-ol ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-5e847a8a4915.svg); 2-methylbutanoic acid ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-c8a1dfddf394.svg); hexan-2-one ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-a62870c62b6d.svg); propyl ethanoate ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-092fada4c1e0.svg).

**Exercise 33.7 ★★.**

Propanal and propanone have the same [molecular formula](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas). Give it. Are they [isomers](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-isomer)? Do they have the same [functional group](#def-g11-functional-groups-functional-group)?

**Solution of Exercise 33.7.**

$\ce{C3H6O}$. Yes, they are [isomers](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-isomer), but with different groups: an [aldehyde](#def-g11-functional-groups-carbonyl) and a [ketone](#def-g11-functional-groups-carbonyl) (both carbonyl groups, in different places).

**Exercise 33.8 ★★.**

Write the [semi-structural formula](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) and the name of the [ester](#def-g11-functional-groups-carboxylic-acid) whose acid part comes from methanoic acid $\ce{HCOOH}$ and whose [alcohol](#def-g11-functional-groups-alcohol) part comes from ethanol; then of the [ester](#def-g11-functional-groups-carboxylic-acid) from ethanoic acid and propan-1-ol.

**Solution of Exercise 33.8.**

$\ce{HCOO-CH2-CH3}$, ethyl methanoate; $\ce{CH3-COO-CH2-CH2-CH3}$, propyl ethanoate.

**Exercise 33.9 ★★.**

Name the [esters](#def-g11-functional-groups-carboxylic-acid) $\ce{CH3-COO-CH3}$, $\ce{CH3-CH2-COO-CH2-CH3}$ and $\ce{HCOO-CH3}$, and give the acid and the [alcohol](#def-g11-functional-groups-alcohol) each is related to.

**Solution of Exercise 33.9.**

Methyl ethanoate (ethanoic acid, methanol); ethyl propanoate (propanoic acid, ethanol); methyl methanoate (methanoic acid, methanol).

**Exercise 33.10 ★★.**

Draw and name the four [alcohols](#def-g11-functional-groups-alcohol) of formula $\ce{C4H10O}$, and give the class of each.

**Solution of Exercise 33.10.**

| ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-0d94d2273dad.svg) | ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-8342403ec7b8.svg) | ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-403ec6726351.svg) | ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-202549bfcb6f.svg) |
| --- | --- | --- | --- |
| butan-1-ol | butan-2-ol | 2-methylpropan-1-ol | 2-methylpropan-2-ol |
| primary | secondary | primary | tertiary |

**Exercise 33.11 ★★.**

Using the table of groups: what is the family of $\ce{CH3-CO-NH2}$? What ending does the name of an [alkene](#def-g11-functional-groups-halogenoalkane) take? Which families have a carbonyl group with an oxygen or nitrogen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) on the same carbon?

**Solution of Exercise 33.11.**

An [amide](#def-g11-functional-groups-amine) (ethanamide). *-ene*. [Carboxylic acids](#def-g11-functional-groups-carboxylic-acid) ($\ce{C=O}$ and $\ce{-OH}$ on the same carbon), [esters](#def-g11-functional-groups-carboxylic-acid) ($\ce{C=O}$ and $\ce{-O-}$) and [amides](#def-g11-functional-groups-amine) ($\ce{C=O}$ and $\ce{N}$): three families.

**Exercise 33.12 ★★★.**

Circle and name the [functional groups](#def-g11-functional-groups-functional-group) of aspirin and of paracetamol. (An $\ce{-OH}$ bonded directly to a ring like that of paracetamol is called a phenol group; it behaves differently from an [alcohol](#def-g11-functional-groups-alcohol).)

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-0c59613ec35f.svg)

**Solution of Exercise 33.12.**

Aspirin: a carboxyl group ([carboxylic acid](#def-g11-functional-groups-carboxylic-acid)) and an [ester](#def-g11-functional-groups-carboxylic-acid) group. Paracetamol: a phenol $\ce{-OH}$ on the ring and an [amide](#def-g11-functional-groups-amine) group $\ce{NH-CO}$.

**Exercise 33.13 ★★★.**

Ethanol $\ce{CH3-CH2-OH}$ and methoxymethane $\ce{CH3-O-CH3}$ have the same [molecular formula](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas). Give it. Methoxymethane belongs to a family not in the table, the ethers. Which of the two can form [hydrogen bonds](https://one-course.com/books/chemistry/1/en/chapter/30-electronegativity-polarity-and-intermolecular-forces#def-g11-polarity-and-cohesion-hydrogen-bond) between its own [molecules](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-molecule)? Which boils higher (one boils at $78\,{}^{\circ}\mathrm{C}$, the other at $-25\,{}^{\circ}\mathrm{C}$)?

**Solution of Exercise 33.13.**

$\ce{C2H6O}$. Only ethanol, with its $\ce{O-H}$, forms [hydrogen bonds](https://one-course.com/books/chemistry/1/en/chapter/30-electronegativity-polarity-and-intermolecular-forces#def-g11-polarity-and-cohesion-hydrogen-bond) between its [molecules](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-molecule) (methoxymethane has no hydrogen on its oxygen). Ethanol boils higher, at $78\,{}^{\circ}\mathrm{C}$; methoxymethane at $-25\,{}^{\circ}\mathrm{C}$.

**Exercise 33.14 ★★★.**

Lactic acid, made by tired muscles, is ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-de60d9d27dfc.svg). Name its two [functional groups](#def-g11-functional-groups-functional-group). When a [molecule](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-molecule) has an acid group and another group, the acid gives the ending and the other group becomes a prefix (*hydroxy-* for $\ce{-OH}$, *amino-* for $\ce{-NH2}$). Name lactic acid, then glycine, $\ce{H2N-CH2-COOH}$.

**Solution of Exercise 33.14.**

A hydroxyl group and a carboxyl group. The chain has three carbons, the acid carbon being carbon 1 and the $\ce{-OH}$ on carbon 2: 2-hydroxypropanoic acid. Glycine: 2-aminoethanoic acid (often written aminoethanoic acid).

**Exercise 33.15 ★★★.**

Wine left open to the [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air) turns into vinegar: ethanol becomes ethanoic acid, through ethanal. Write the semi-structural and [molecular formulas](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) of the three compounds and their families. What changes in the formula at each step?

**Solution of Exercise 33.15.**

Ethanol $\ce{CH3-CH2-OH}$, $\ce{C2H6O}$, [alcohol](#def-g11-functional-groups-alcohol); ethanal $\ce{CH3-CHO}$, $\ce{C2H4O}$, [aldehyde](#def-g11-functional-groups-carbonyl); ethanoic acid $\ce{CH3-COOH}$, $\ce{C2H4O2}$, [carboxylic acid](#def-g11-functional-groups-carboxylic-acid). From ethanol to ethanal two hydrogen [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) are lost; from ethanal to ethanoic acid one oxygen [atom](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) is gained.

## 33.7 Problem: Fruit Flavours

**Problem 33.1.**

Weekend problem — a flavour chemist builds the smell of banana: what is the molar mass of the key molecule?

A flavour chemist has five compounds on her bench:

| A | ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-bccdd0c9a600.svg) |
| --- | --- |
| B | ![](https://one-course.com/images/onecourse/chapters/chemistry-1/g11-functional-groups/fig-748c72fda77c.svg) |
| C | $\ce{CH3-COOH}$ |
| D | $\ce{CH3-CH2-CH2-CH2-CH2-CHO}$ |
| E | $\ce{CH3-CH2-CH2-COO-CH2-CH3}$ |

A smells of banana and pear drops, B of malt, C of vinegar, D of cut grass, E of pineapple.

**Part I — Groups and families.**

1. Name the [functional group](#def-g11-functional-groups-functional-group) of each compound.
2. Give the family of each.
3. Which compounds are [esters](#def-g11-functional-groups-carboxylic-acid) ? Which smells do they have?
4. What is the class of the [alcohol](#def-g11-functional-groups-alcohol) B?
5. Give the [molecular formula](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) of D, and draw an isomer of D that is a [ketone](#def-g11-functional-groups-carbonyl) .

**Part II — Names.**

6. Name B (find the longest chain that holds the carbon bearing $\ce{-OH}$ ).
7. Name C and D.
8. Name E, and give the acid and the [alcohol](#def-g11-functional-groups-alcohol) it is related to.
9. Explain the name of A, 3-methylbutyl ethanoate: which part comes from the acid, which from the [alcohol](#def-g11-functional-groups-alcohol) ?

**Part III — From an acid and an [alcohol](#def-g11-functional-groups-alcohol).**

10. To which two compounds of the bench is A related?
11. Give the [molecular formulas](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) of A, B and C.
12. An [ester](#def-g11-functional-groups-carboxylic-acid) is made from its acid and its [alcohol](#def-g11-functional-groups-alcohol) with loss of one small [molecule](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-molecule) . Using the formulas, find which.
13. Write the equation of the formation of A, in [molecular formulas](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-formulas) , and check that it is balanced.

**Part IV — Molar masses.**

14. Compute the molar masses of B and C.
15. Deduce the [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass) of A from the equation of question 13.
16. Compute the [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass) of A directly from its formula, and compare.
17. An unknown fruity sample is found to have a [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass) close to $116\,\mathrm{g}/\mathrm{mol}$ . Is it A or E?
18. Heptanoic acid, $\ce{CH3-(CH2)5-COOH}$ , smells rancid. Show that it is an isomer of A. Can a [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass) alone identify a compound?
19. Why do chemists say the smell belongs to the [functional group](#def-g11-functional-groups-functional-group) as much as to the skeleton? Use A and heptanoic acid.
20. State the final answer: what is the [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass) of the banana [ester](#def-g11-functional-groups-carboxylic-acid) , 3-methylbutyl ethanoate?

**Solution of Problem 33.1.**

**1.** A: [ester](#def-g11-functional-groups-carboxylic-acid) group; B: hydroxyl; C: carboxyl; D: carbonyl at the end of the chain; E: [ester](#def-g11-functional-groups-carboxylic-acid) group.

**2.** A [ester](#def-g11-functional-groups-carboxylic-acid), B [alcohol](#def-g11-functional-groups-alcohol), C [carboxylic acid](#def-g11-functional-groups-carboxylic-acid), D [aldehyde](#def-g11-functional-groups-carbonyl), E [ester](#def-g11-functional-groups-carboxylic-acid).

**3.** A (banana) and E (pineapple): fruity smells.

**4.** Primary: the carbon bearing $\ce{-OH}$ is bonded to one carbon.

**5.** $\ce{C6H12O}$; for example hexan-2-one, $\ce{CH3-CO-CH2-CH2-CH2-CH3}$.

**6.** The chain holding the $\ce{C-OH}$ has four carbons, numbered from the $\ce{-OH}$, with a methyl on carbon 3: 3-methylbutan-1-ol.

**7.** C: ethanoic acid; D: hexanal.

**8.** Ethyl butanoate, related to butanoic acid and ethanol.

**9.** *Ethanoate*: the acid part $\ce{CH3-CO}$, from ethanoic acid; *3-methylbutyl*: the [alcohol](#def-g11-functional-groups-alcohol) part, from 3-methylbutan-1-ol.

**10.** C (ethanoic acid) and B (3-methylbutan-1-ol).

**11.** A $\ce{C7H14O2}$; B $\ce{C5H12O}$; C $\ce{C2H4O2}$.

**12.** $\ce{C2H4O2} + \ce{C5H12O}$ contains $\ce{C7H16O3}$, one $\ce{H2O}$ more than $\ce{C7H14O2}$: water.

**13.** $\ce{C2H4O2 + C5H12O -> C7H14O2 + H2O}$: C 7 = 7, H 16 = 16, O 3 = 3.

**14.** $M(\text{B}) = 5 \times 12.0 + 12 \times 1.0 + 16.0 =
88.0\,\mathrm{g}/\mathrm{mol}$; $M(\text{C}) = 60.0\,\mathrm{g}/\mathrm{mol}$.

**15.** $60.0 + 88.0 - 18.0 = 130.0\,\mathrm{g}/\mathrm{mol}$.

**16.** $7 \times 12.0 + 14 \times 1.0 + 2 \times 16.0 =
130.0\,\mathrm{g}/\mathrm{mol}$: the same.

**17.** E, $\ce{C6H12O2}$: $6 \times 12.0 + 12 \times 1.0 + 2 \times
16.0 = 116.0\,\mathrm{g}/\mathrm{mol}$.

**18.** $\ce{C7H14O2}$: same formula as A, so an isomer, with the same [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass). A [molar mass](https://one-course.com/books/chemistry/1/en/chapter/25-the-mole-and-molar-mass#def-g10-the-mole-molar-mass) alone cannot tell [isomers](https://one-course.com/books/chemistry/1/en/chapter/32-organic-molecules-skeletons-and-names#def-g11-organic-skeletons-isomer) apart.

**19.** A and heptanoic acid have the same [atoms](https://one-course.com/books/chemistry/1/en/chapter/11-atoms-and-molecules#def-g7-atoms-and-molecules-atom) but different groups, an [ester](#def-g11-functional-groups-carboxylic-acid) and a [carboxylic acid](#def-g11-functional-groups-carboxylic-acid): one smells of banana, the other rancid. The group, and where it sits, decides.

**20.** $130.0\,\mathrm{g}/\mathrm{mol}$.