Organic chemistry

Question 1

What are the two types of isomers

Answer 1

Structural isomers

stereoisomers

Question 2

What are the two types of structural isomers

Answer 2

Structural isomers are isomers with the same molecular formula bonded together in different arrangements, chain and positional isomers

Question 3

What are chain isomers

Answer 3

They are the consequence of a branching alkyl group

Question 4

What are positional isomers

Answer 4

They can occur for organic molecules that contain functional groups, the functional group can be attached to a different location

Question 5

What are stereoisomers

Answer 5

They are isomers in which the atoms in two molecules are connected in the same order but have different arrangements in space

Question 6

Do stereoisomers have different chemical properties?

Answer 6

They differ in their 3D shape and they can have very different chemical properties

Question 7

What are optical isomers

Answer 7

They have a different placement of groups around one atom in a molecule. The molecules have identical molecular and semistructual formal.

Question 8

Are optical isomers chiral

Answer 8

Optical isomers are said to be chiral, two objects are chiral when they are mirror images of each other and the mirror images cannot be superimposed

Question 9

What area chiral objects

Answer 9

Chiral objects have mirror images which are superimposable

Question 10

What is the requirement for a chiral molecule

Answer 10

A carbon atom joined to four different groups in a tetrahedral arrangement.

Question 11

What are a pair of chiral molecules called

Answer 11

Enantiomers

Question 12

What difference is there between the properties of chiral molecules

Answer 12

Enantiomers have identical physical properties apart from the way they rotate plane polarised light. Same melting and boiling points and the same solubility in water.

Question 13

What are geometric isomers

Answer 13

These isomers occur where restricted rotation can occur about a carbon carbon double bond. Cis trans isomers

Question 14

Define flash point

Answer 14

The lowest temperature at which a liquid will produce a vapour that will ignite to produce a flame when an ignition source is applied

Question 15

What happens to hydrocarbons physical properties are molar mass increases

Answer 15

As Mr increases dispersion forces become stronger. Bp increases, viscosity increases, flashpoint increases, volatility decreases

Question 16

What happens to physical properties of isomers with branches compared to non branched isomers

Answer 16

Liner isomers: they are more compact, molecules are closer and they have stronger intermolecular forces, dispersion forces.

Non liner isomers: as the molecule are far apart, weaker intermolecular forces, dispersion forces. Boiling point decreases, viscosity decreases, volatility increases, flashpoint decreases

Question 17

What do stronger intermolecular forces cause

Answer 17

Greater boiling points, greater flash points and high viscosity and lower volatility

Question 18

Do hydrocarbons dissolve in water

Answer 18

Hydrocarbons are on polar, therefore they do not dissolve in polar h2O, it simply forms a layer of separation. The top layer is hydrocarbons and h2o is denser

Question 19

What is the difference in physical properties from an alkene to an alkyne

Answer 19

Mr decreases, therefore weaker dispersion forces. Physical properties decreases expect for volatility

Question 20

What is the difference between physical properties from hydrocarbons and haloalkanes

Answer 20

the carbon chlorine bond in chloromethane is polar because the chlorine atom is more electectronegative that the carbon atom.
The presence of these permanent dipole allows for the formation of dipole-dipole attractions between chloromethane molecules

Question 21

Are haloalkanes soluble in water

Answer 21

They are slightly more soluble than hydrocarbons in h2o. But the solubility is still very low because the overalll influence of the dipole dipole interaction is small.

Question 22

What happens to solubility of haloalkane as carbon chain length increases

Answer 22

The influence of the halogen decreases as the carbon chain length increases, haloalkanes become less soluble in h2o with increasing chain length as non polar character increases

Question 23

Are haloalkanes more dense that h2o

Answer 23

They are denser than h2o and settle to form a layer at the bottom when added to water when it is insoluble or saturated

Question 24

Which homologous series can form hydrogen bonds

Answer 24

alcohol, carboxylic acids, amines, amides

Question 25

Compare intermolecular forces of alcohols and carboxylic acids

Answer 25

There is no dimerisation between alcohols. Therefore H bonding gin alcohols is weaker than carboxylic acids. strong H bonds due to dimerisation

Question 26

Explain why carboxylic acids may not be a good fuel compared to alcohols (compounds have similar molar masses)

Answer 26

Alcohols are a better fuel than carboxylic acids. Carboxylic acids dimerise, therefore their H bondings are stronger, flashpoint is higher. Alcohols do not dimerise hence weaker H bonding, lower flashpoint. The lower the flashpoint, the fuel which has this will be a better fuel.

Question 27

Why are haloalkanes and amines not used as fuels

Answer 27

Upon combustion of haloalkanes they release halo oxides while amides release toxic oxides of nitrogen.

Question 28

Explain the intermolecular bonding in amines

Answer 28

-Nitrogen is less electronegative compared to oxygen. Therefore H bonding in amines is weaker than alcohol and weaker than amides

Question 29

Explain the intermolcular bonding in amides

Answer 29

• More number of hydrogen bonds between amide molecules forming
• H bonds produced by oxygen will be stronger due to higher electronegativity

Question 30

Explain the solubility in water of an alcohol

Answer 30

• H bonding between water and alcohol means it readily dissolves in water
• Longer the R group in the alcohol, it has more non polar characteristics therefore solubility in water decreases

Question 31

Explain solubility in water of amines

Answer 31

Due to less electronegativity of H, H bonding forms with water, weaker than that of an alcohol

Question 32

`Explain solubility in water of acids

Answer 32

Acids ionise in water as a result of ionisation they produce RCOO- and H3O+ so ionic interactions form when dissolved in water

Question 33

Which homologous series only form dipole dipole and dispersion

Answer 33

Aldehydes, keytones and esters

Question 34

Which fuel is better, methane or fluoromethane?

Answer 34

Methane: non polar, intermolecular forces are dispersion only, lower flashpoint, product of complete combustion is Co2 and h2O

Fluoromethane: polar, intermolecular forces are dipole-dipole and dispersion, higher flashpoint, products of combustion are co2 h2o and fluorooxides which is toxic.
therefore methane is a better fuel that fluoromethane

Question 35

What is needed for a substituition reaction and why

Answer 35

Uv light is needed and it is and energy source to overcome Ea of substitution reaction

Question 36

Alkene to alkane reaction

Answer 36

Needs Ni(catalyst). Breaks double bond

Question 37

Alkene to alcohol

Answer 37

Needs h3PO4/300 degrees and requires a H2O molecule to break the bond and create an alcohol

Question 38

Alkene to haloalkane

Answer 38

Needs X2 and the X goes on opposite sides of carbon atoms

Question 39

What is needed to oxidise alcohols

Answer 39

Potassium dichromate (K2Cr2O7) and potassium permanganate (KMnO4)

Question 40

Oxidising a primary alcohol

Answer 40

Aldehyde and if heated, carboxylic acid

Question 41

Oxidation of secondary alcohols

Answer 41

Keytone is produced where the OH bond used to be

Question 42

Why do tertiary alcohols not oxidise

Answer 42

During oxidation of alcohols there is an increase in the number of C-O bonds and a simultaneous decrease at the same carbon atom in the number of C-H bonds/ In tertiary alcohols the carbon attached to the hydroxy group does not have a C-H bond to break so oxidation cannot occur at that carbon atom.

Question 43

Reaction of carboxylic acid with primary amide

Answer 43

primary amides can be prepared by the reaction of a carboxylic acid with ammonia. Condensation reaction

Question 44

Reaction of carboxylic acid with primary amine

Answer 44

secondary amide plus h2o. Amide link is formed in this reaction

Question 45

Markovnikov’s rule

Answer 45

The most electronegative functional group will be added to the carbon attached to the least number of H’s in a an addition reaction.

Question 46

Of a cis and trans isomer which would have a higher melting point and why?

Answer 46

Tran would have a higher melting point as it isn able to pack more closely therefore stronger dispersion forces that require more heat energy to overcome. These override the relatively strong dipole dipole forced in the polar cis form (trans in non polar so dispersion forces only)

Question 47

Of a cis and trans isomer which would have a higher boiling point and why?

Answer 47

Cis as it is a polar molecule. Therefore it has dipole dipole interactions between them that are stronger than the dispersion forces in the non polar trans form. In a liquid packing of the molecules has no effect. dipole dipole forces require more heat energy to break than the dispersion forces.

Question 48

Order or priority for naming organic compounds

Answer 48

1. carboxyl
2. hydroxyl
3. Amino
4. double or triple carbon bonds
5. halogens and alkyl branches (equal)