3.3.1. Formulae, isomerism and mechanisms

Question 1

What is an empirical formula?

Answer 1

The simplest whole number ratio of atoms of each element in a compound

Question 2

What is a molecular formula?

Answer 2

The formula that shows the actual number of atoms of each element in a molecule

Question 3

What is a general formula?

Answer 3

A generalised formula which enables you to work out the molecular formula of a compound within a homologous series

Question 4

What is a structural or shorthand formula?

Answer 4

A formula showing the arrangement of atoms in a substance without showing the bonds. E.g. CH?CH?CH?

Question 5

What is a displayed formula?

Answer 5

A formula showing the arrangement of atoms in a substance and all the bonds E.g.

Question 6

What is a skeletal formula?

Answer 6

A simplified version of a displayed formula where straight lines represent carbon-carbon bonds e.g.

Question 7

What is a hydrocarbon?

Answer 7

A compound made of atoms of hydrogen and carbon only

Question 8

What is an alkane?

Answer 8

A hydrocarbon with only single bonds.

Question 9

What is isomerism?

Answer 9

When molecules have the same atoms but they are arranged differently

Question 10

What are the two main types of isomerism?

Answer 10

Structural isomerism and stereoisomerism

Question 11

What is structural isomerism?

Answer 11

Where isomers have the same molecular formula but a different structure

Question 12

What is chain isomerism?

Answer 12

Compounds that have the same molecular formula but the longest carbon chain differs

Question 13

What is position isomerism?

Answer 13

Compounds that have the same molecular formula but the functional group is attached to the chain in a different position

Question 14

What is functional group isomerism?

Answer 14

Compounds that have the same molecular formula but there are different functional groups

Question 15

What is stereoisomerism?

Answer 15

Where isomers have the same structural formula but are arranged differently in 3D space

Question 16

What are the two types of stereoisomerism?

Answer 16

E/Z isomerism and optical isomerism

Question 17

Why can E/Z isomers exist?

Answer 17

The C=C double bond can’t rotate

Question 18

What conditions does a molecule need to fulfil to exhibit E/Z isomerism?

Answer 18

C=C double bond and each carbon atom needs to have two different groups attached

Question 19

What is a chiral carbon?

Answer 19

Carbon atom with four different groups surrounding it

Question 20

What conditions does a molecule need to fulfil to exhibit optical isomerism?

Answer 20

Contain a chiral carbon

Question 21

What are enantiomers?

Answer 21

Molecules with the same structural formula but exhibiting optical isomerism

Question 22

What is the effect of two enantiomers on plane polarized light?

Answer 22

They rotate it in opposite directions

Question 23

What is a racemic mixture?

Answer 23

A 50:50 mixture of two enantiomers

Question 24

Explain the effect of a racemic mixture on plane polarized light

Answer 24

One enantiomer rotates the light clockwise and the other anti-clockwise, resulting in no net rotation.

Question 25

In a mechanism, what do curly arrows show?

Answer 25

The movement of electrons

Question 26

In a mechanism, where do curly arrows go from/to?

Answer 26

From electron sources (bond or lone pair) to electron sinks (atom/molecule/ion that can accept a new bond/lone pair)

Question 27

What is a nucleophile?

Answer 27

Electron rich species that contain an electron pair available for bonding

Question 28

Give examples of common nucleophiles

Answer 28

Ammonia, hydroxide ions, cyanide ions, water, alcohols, amines

Question 29

What is an electrophile?

Answer 29

Electron poor species that seek an electron pair available for bonding

Question 30

Give examples of common electrophiles

Answer 30

Hydrogen halides, halogen molecules, H2SO4, nitronium ion, acylium ions

Question 31

What is an addition mechanism?

Answer 31

Where the number of groups around the carbon atom increases

Question 32

What is a substitution mechanism?

Answer 32

Where the number of groups around the carbon atom stays the same, occuring in one step

Question 33

What is an elimination mechanism?

Answer 33

Where the number of groups around the carbon atom decreases

Question 34

What is an addition-elimination mechanism?

Answer 34

Where the number of groups around the carbon atom stays the same, occuring in two steps

Question 35

What compounds undergo electrophilic addition?

Answer 35

Alkenes

Question 36

What compounds undergo nucleophilic substitution?

Answer 36

Haloalkanes

Question 37

What compounds undergo elimination?

Answer 37

Haloalkanes, alcohols

Question 38

What compounds undergo nucleophilic addition-elimination reactions?

Answer 38

Acyl chlorides, aldehydes, ketones, acid anhydrides

Question 39

What compounds undergo electrophilic substitution?

Answer 39

Aromatic compounds