An Introduction to A-Level Organic Chemistry

Question 1

Aromatic compounds

Answer 1

-molecules that consist of one or more rings with conjugated π systems
-are called ‘aromatic’ as they often have pleasant odours

Question 2

Conjugated π systems

Answer 2

arise from alternating double and single bonds in which the electrons are delocalised

Question 3

Functional group

Answer 3

an atom or group of atoms in an organic molecule, that determines its characteristic chemical and physical properties

Question 4

Arenes

Answer 4

aromatic compounds that contain a benzene ring

Question 5

Chemical properties of arenes

Answer 5

-Due to the delocalised electron ring, arenes are electron-rich and therefore can undergo electrophilic attack under the right conditions.
-However the delocalised electron ring system also makes benzene so stable to the extent that it is resistant to addition reactions, thus they are different to alkenes, which are very reactive and readily undergo addition reactions

Question 6

Physical properties of arenes

b.p, IMF, solubility

Answer 6

-Benzene has van der Waals dispersion forces of attraction between the molecules and has a boiling point of 80 C
-Because of the presence of the non-polar hydrocarbon part in the arene functional group, these compounds are often insoluble in water
-Benzene isn’t soluble in water because it would have to break many hydrogen bonds between the water molecules to dissolve which doesn’t happen because it isn’t energetically favourable

Question 7

Halogenoarenes

Answer 7

aromatic compounds that contain a halogen bonded to a benzene ring

Question 8

Another name for halogenoarenes

Answer 8

aryl halides

Question 9

Chemical properties of halogenoarenes

Answer 9

-compounds prone to electrophilic attack because of the π system of delocalised electrons
-the halogens can also take part in substitution reactions

Question 10

Physical properties of halogenoarenes

condition at r.t.p, b.p, solubility

Answer 10

-Chlorobenzene, bromobenzene and iodobenzene are all liquid at room temperature with an oily texture
-The boiling points increase as the size of the halogen attached increases because the number of electrons within the molecule increases
-Insoluble in water because of the non-polar hydrocarbon part of the ring
-Molecules are large relative to the size of water molecules, and it is not energetically favourable for the halogenoarene molecules to break the hydrogen bonds between the water molecules in order to dissolve

Question 11

Phenols

Answer 11

a type of aromatic compounds containing a hydroxide bonded to a benzene ring

Question 12

Chemical properties of phenols

acidity, reactivity, reactions

Answer 12

-The -OH group in phenols is more acidic than in alcohols as the oxygen donates one of its lone pairs of electrons into the ring system
-This causes an increased electron density of the ring, causing it to become much more reactive than benzene itself
-It also makes it easier for the hydrogen of the -OH group to be donated
-Phenols can also react with reactive metals such as sodium to form alkoxide ions

Question 13

Physical properties of phenols

Answer 13

-Phenol is a white, crystalline solid, and it has a disinfectant-like smell
-Due to the -OH group in phenols, they can form hydrogen bonds with water molecules, and therefore to a degree phenol is soluble in water

Question 14

Acyl chlorides

Answer 14

carboxylic acid derivatives containing:
-A chlorine atom attached to a C=O group (replacing what would have been the -OH group of a carboxylic acid)
-An acyl (hydrocarbon) group attached to a C=O group

Question 15

Another name for acyl chlorides

Answer 15

acid chlorides

Question 16

Chemical properties of acyl chlorides

Answer 16

-They are fuming liquids and are colourless, with a strong smell
-Acyl chlorides are extremely reactive and readily take part in substitution reactions in which the chlorine atom is substituted by other species
-This reactivity is why they are fuming liquids and why they have such a strong smell - they react with any water vapour in the air

Question 17

Physical properties of acyl chlorides

Answer 17

Acyl chlorides react violently with water, so we cannot say whether or not they would be soluble in water

Question 18

Amines

Answer 18

compounds with the -NH2 (primary amine), -NH (secondary amine) or -N (tertiary amine) group

Question 19

Classification of amines

Answer 19

-In primary amines, the N of the amine group is bonded to one R group (and two hydrogen atoms)
-In secondary amines, the N of the amine group is bonded to two R groups (and one hydrogen atom)
-In tertiary amines, the N of the amine group is bonded to three R groups

Question 20

Chemical properties of amines

Answer 20

Due to the lone pair of electrons on the nitrogen, amines are basic compounds

Question 21

Physical properties of amines

Answer 21

-The lone pair on the N of the amine group means that they can form hydrogen bonds
-They are often soluble in water because they form hydrogen bonds with water molecules
-The smaller amines are very soluble in water, but their solubility decreases as the non-polar hydrocarbon chain gets longer
-They often have a fishy smell, especially as the size of the amines increases

Question 22

Amides

Answer 22

compounds containing:
-An amine (-NH2) group
-A carbonyl group (C=O)

The amide group is -CONH2

Question 23

Chemical properties of amides

Answer 23

Amides are less basic than amines, as the lone pair of electrons on the nitrogen is delocalised

Question 24

Physical properties of amides

Answer 24

-Amides are often soluble in water as they can form hydrogen bonds with water molecules
-The smaller amides are very soluble in water, but their solubility decreases as the non-polar hydrocarbon chain gets longer

Question 25

Amino acids

Answer 25

building blocks of proteins and consists of:
-An amine (-NH2) group
-A carboxyl (-COOH) group

Question 26

Chemical properties of amino acids

Answer 26

-react with bases to form salts
-react with alcohols to form esters
-react with amines to gives amides

Question 27

Physical properties of amino acids

Answer 27

-soluble in water but insoluble in organic solvents
-have chiral centres and exhibit optical isomers (except for glycine)

Question 28

General Formula of Arenes

Answer 28

CnH2n-6M

n=number of C atoms m=number of rings

Question 29

General Formula of Halogenoarenes

Answer 29

CnH2n-7mX

Question 30

General Formula of Phenols

Answer 30

CnH2n-7mOH

Question 31

General Formula of Acyl Chlorides

Answer 31

RCOCl

Question 32

General Formula of Amines

Answer 32

CnH2n+3N

Question 33

General Formula of Amides

Answer 33

RCONH2

Question 34

General Formula of Amino Acids

Answer 34

HOOCCHRNH2

Question 35

naming organic compounds: aliphatic compounds

Answer 35

1)Identify the longest carbon chain containing the functional group
2)Identify the functional group on the chain to determine the suffix or prefix on the compound
3)Count along the carbon chain such that the functional group has the lowest number
4)Add any side chains or lower priority functional groups as prefixes to the beginning of the name in alphabetic order
5)Use the prefixes di-, tri- and tetra- if there are two or more identical functional groups or side chains

Question 36

Electrophiles

Answer 36

‘electron loving’ species that are electron deficient and can act as an electron pair acceptor

Question 37

Substitution reactions

Answer 37

reactions that involve the replacement of one atom or group of atoms by another

Question 38

Electrophilic substitution reactions

Answer 38

reactions in which an atom or group of atoms are replaced by an electrophile after initial attack by the electron-deficient species

Question 39

Addition reactions

Answer 39

reactions in which two or more molecules combine to give a single product only

Question 40

Elimination reactions

Answer 40

the reverse of addition reactions; a small molecule (such as H2O or HCl) is removed or ‘eliminated’ from an organic molecule

Question 41

The shape of benzene & aromatic compounds

Answer 41

-contain sp2 hybridised carbons as two of their p orbitals have mixed with an s orbital
-each carbon atom in the ring forms three σ bonds using the sp2 orbitals
-remaining p orbital overlaps laterally with p orbitals of neighbouring carbon atoms to form a π bond resulting in the electrons being delocalised and being able to spread over the entire ring freely
-are regular and planar compounds with bond angles of 120 degrees
-delocalisation of electrons means that all of the carbon-carbon bonds in these compounds are identical and have both single and double bond characters; bonds are all the same length

Question 42

Stereoisomers

Answer 42

are molecules that have the same structural formula but have the atoms arranged differently in space

Question 43

Two types of stereoisomers

Answer 43

Geometrical (cis/trans) and Optical

Question 44

Optical isomerism

Answer 44

A carbon atom that has four different atoms or groups of atoms attached to it is called a chiral carbon or chiral centre

Question 45

enantiomers

Answer 45

optical isomers that are mirror images of each other and are non-superimposable

Question 46

similarities and differences between enantiomers

Answer 46

-their physical and chemical properties are identical
-differ in their ability to rotate plane polarised light
-differ from each other in terms of their biological activity

Question 47

Biological activity of enantiomers

Answer 47

-Enzymes are chiral proteins that speed up chemical reactions by binding substrates
-They are very target-specific as they have a specific binding site and will only bind molecules that have the exact same shape
-Therefore, if one enantiomer binds to a chiral enzyme, the mirror image of this enantiomer will not bind nearly as well if at all

Question 48

optically active mixture

Answer 48

-When a solution contains an uneven mixture of each enantiomer
-For example, 20% of a solution contains an enantiomer that rotates the plane of polarised light clockwise and 80% of the solution has an enantiomer that rotates the plane of polarised light anticlockwise; the net effect is that the plane of polarised light will be rotated anticlockwise

Question 49

racemic mixture

Answer 49

a mixture in which there are equal amounts of enantiomers present in the solution so plane polarised light remains unchanged

Question 50

R enantiomer

Answer 50

the enantiomer that rotates the plane polarised light clockwise

Question 51

S enantiomer

Answer 51

the enantiomer that rotates the plane polarised light anticlockwise

Question 52

How can the identity of an optical isomer of a single substance be identified?

Answer 52

using the rotation of plane-polarised light, depending on which isomer the sample contains, the plane of polarised light will be rotated either clockwise or anti-clockwise

Question 53

Why is it important that only one enantiomer of the optical isomer be produced when manufacturing drugs

Answer 53

-to increase the drugs’ effectiveness
-to avoid drug enantiomers that have very harmful side effects

Question 54

What happens when conventional organic reactions are used to make the desired drug

Answer 54

a racemic mixture will be obtained

Question 55

examples of drug chirality affecting its effectiveness

Answer 55

-the drug naproxen is used to treat pain in patients that suffer from arthritis; one of the enantiomers of naproxen eases the pain while the other enantiomer causes liver damage
-one enantiomer of a drug used to treat tuberculosis is effective whereas another enantiomer of this drug can cause blindness
-thalidomide is another example of a drug that used to be used to treat morning sickness, where one of the enantiomers caused very harmful side effects for the unborn baby

Question 56

Why it’s very important to separate a racemic mixture into pure single enantiomers when they are being put in the drug product

Answer 56

• reduced side effects in patients; it protects pharmaceutical companies from legal actions if the side effects are too serious
  -decreases the patient’s dosage by half as the pure enantiomer is more potent and therefore reduces production costs; a more potent drug has a better therapeutic activity

Question 57

What should be used in order to produce single, pure optical isomers

Answer 57

chiral catalysts

Question 58

benefits of using chiral catalysts

Answer 58

only small amounts of them are needed and they can be reused

Question 59

why are enzymes excellent biological chiral catalysts

Answer 59

they promote stereoselectivity and produce single-enantiomer products only

Question 60

Stereoselectivity

Answer 60

refers to the preference of a reaction to form one enantiomer over the other

Question 61

How enzymes help in promoting stereoselectivity and produce single-enantiomer products only

Answer 61

-Due to the specific binding site of enzymes, only one enantiomer is formed in the reaction
-The enzymes are fixed in place on inert supports so that the reactants can pass over them without having to later separate the product from the enzymes

Question 62

the disadvantages of using enzymes to produce single-enantiomer products only and how to counterattack it

Answer 62

-it can be expensive to isolate them from living organisms; therefore, more research has recently been carried out into designing synthetic enzymes
-using enzymes takes longer than conventional synthetic routes however using enzymes is also a greener process as fewer steps are involved compared to conventional synthetic routes