module 4: core organic chemistry

Question 1

what are structural isomers?

Answer 1

compounds with the same molecular formula but different structural formulae

Question 2

what is a hydrocarbon?

Answer 2

a compound that contains only hydrogen and carbon

Question 3

what does saturated mean?

Answer 3

containing single bonds only

Question 4

what does unsaturated mean?

Answer 4

containing a double carbon-carbon bond

Question 5

what is a skeletal formula?

Answer 5

a simplified organic formula

Question 6

what is a homologous series?

Answer 6

a series of organic compounds with the same functional group (similar chemical properties) whose successive members differ by the addition of a -CH2- group

Question 7

what is the general formula for alkanes?

Answer 7

CnH2n+2

Question 8

what are alkanes?

Answer 8

saturated hydrocarbons

Question 9

what are alkenes?

Answer 9

unsaturated hydrocarbons

Question 10

what is a functional group?

Answer 10

the part of the organic molecule responsible for its chemical reactions

Question 11

what are the products of the complete combustion of alkanes?

Answer 11

carbon dioxide + water

Question 12

what are the products of the incomplete combustion of alkanes?

Answer 12

carbon monoxide (or carbon) + water

Question 13

describe the reactions of alkanes with halogens

Answer 13

• alkanes react with halogens, but only in the presence of sunlight
• high energy UV radiation present in sunlight provides the initial energy for a reaction to take place

Question 14

what type of reaction is that of alkanes with halogens?

Answer 14

a substitution reaction - a hydrogen atom in the alkane is substituted by a halogen atom

Question 15

what are the three stages that make up the mechanism of the bromination of alkanes?

Answer 15

step 1 = initiation
step 2 = propagation
step 3 = termination

Question 16

describe what happens in the first stage of the bromination of alkanes

Answer 16

stage 1 = initiation
- the reaction is started when the covalent bond in a bromine molecule is broken down by homolytic fission
- each bromine atom takes one electron from the pair, forming two highly reactive bromine radicals
- energy for this bond fission is provided by UV radiation

Br - Br –> Br* + Br*

Question 17

what is a radical?

Answer 17

a very reactive species with an unpaired electron

Question 18

describe what happens in the second stage of the bromination of alkanes

Answer 18

stage 2 = propagation
- the reaction propagates through two propagation steps, a chain reaction

Propagation step 1: CH₄ + Br* –> ·CH3 + HBr
Propagation step 2: ·CH3 + Br2 –> CH3Br + Br*

Question 19

what happens in the first propagation step?

Answer 19

a bromine radical reacts with a C - H bond in the methane, forming a methyl radical and a molecule of hydrogen bromide

Question 20

what happens in the second propagation step?

Answer 20

each methyl radical reacts with another bromine molecule, forming bromomethane and a new bromine radical

Question 21

describe what happens in the third stage of the bromination of alkanes

Answer 21

• two radicals collide, forming a molecule with all electrons paired
• there are a number of possibilities
• when two radicals collide and react, both radicals are removed from the reaction mixture, stopping the reaction

Question 22

what can hydrocarbons be classified as?

Answer 22

• aliphatic
• aromatic
• alicyclic

Question 23

what are aliphatic hydrocarbons?

Answer 23

carbon atoms are joined to each other in an unbranched (straight) or branched chains, or non-aromatic rings

Question 24

what are alicyclic hydrocarbons?

Answer 24

carbon atoms are joined to each other in ring (cyclic) structures, with or without branches

Question 25

what are aromatic hydrocarbons?

Answer 25

some or all of the carbon atoms are found in a benzene ring

Question 26

what is homolytic fission?

Answer 26

the breaking of a covalent bond where each of the bonded atoms take one of the shared pair of electrons from the bond

Question 27

what is heterolytic fission?

Answer 27

the breaking of a covalent bond where one of the bonded atoms takes both of the electrons from the bond

Question 28

what are the two types of bond fission?

Answer 28

homolytic and heterolytic fission

Question 29

in a reaction mechanism, what do curly arrows represent?

Answer 29

movement of electron pairs when bonds are being broken or made

Question 30

what is a sigma bond?

Answer 30

the direct overlap of two orbitals

Question 31

what is a pi bond?

Answer 31

the sideways overlap of two p-orbitals

Question 32

explain the effect of increasing chain length on the boiling points of alkanes

Answer 32

- increased chain length - greater surface area of contact - stronger london forces - more energy required to overcome these forces - boiling point increases

Question 33

explain the effect of branching on the boiling points of alkanes

Answer 33

- more branching - less surface area of contact - weaker london forces - less energy required to overcome these forces - boiling point decreases

Question 34

what is a nucleophile?

Answer 34

an electron pair donor

Question 35

what is an electrophile?

Answer 35

an electron pair acceptor

Question 36

state and explain how the rates of hydrolysis of the chloroalkane and the bromoalkane would differ

Answer 36

- rate slower with the chloroalkane - C-Cl bond is stronger than C-Br bond

Question 37

what are the reagents and conditions for an alkene to alcohol reaction?

Answer 37

steam and acid catalyst

Question 38

what are the reagents and conditions for an alkane to haloalkane?

Answer 38

halogen and UV

Question 39

state what is meant by the term ionic bond

Answer 39

electrostatic attraction between positive and negative ions

Question 40

describe the use of aqueous barium chloride in qualitative analysis

Answer 40

- test for sulfate ions - white precipitate forms

Question 41

describe the oxidation reactions of butan-1-ol forming an aldehyde and carboxylic acid

Answer 41

oxidation reaction forming an aldehyde: - acidified potassium dichromate - heat and distillation - organic product is butanal oxidation reaction forming a carboxylic acid: - acidified potassium dichromate - heat under reflux - organic product is butanoic acid

Question 42

suggest the general formula for a carboxylic acid

Answer 42

CnH2n+1COOH

Question 43

what are the differences between pi and sigma bonds?

Answer 43

- a sigma bond is between bonding atoms and a pi bond is above and below the bonding atoms - a sigma bond has direct overlap of orbitals and pi bond has sideways overlap of orbitals - pi bond has a lower bond enthalpy - sigma bond has electron density between bonding atoms and pi bond has electron density above and below bonding atoms

Question 44

what are the reagents for an alcohol to haloalkane reaction?

Answer 44

sodium halide and sulfuric acid

Question 45

what are the reagents for an alkene to haloalkane reaction?

Answer 45

hydrogen halide

Question 46

what are the reagents for an alcohol to alkene reaction?

Answer 46

concentrated sulfuric acid

Question 47

what are the reagents for an alkene to alkane reaction?

Answer 47

H₂ and nickel catalyst