1.7 introductory organic chemistry

Question 1

1b: Complete 5 molecule drawings generated from the spreadsheet.

Answer 1

How many did you get right? Rank below:

Question 2

1c: What is the difference between a hazard and a risk?

Answer 2

a risk is the likelihood of a hazard

Question 3

2a: What is an alkane?

Answer 3

a saturated hydrocarbon (only has C and H with single bonds)

Question 4

2a: What is the general formula of alkanes?

Answer 4

CnH2n+2

Question 5

2b: What are isomers?

Answer 5

molecules with the same molecular formula but a different structural formula

Question 6

2c: What are alkanes generally used for?

Answer 6

fuels

Question 7

2c: Whence are alkanes obtained?

Answer 7

crude oil

Question 8

2c: How is a certain alkane extracted from crude oil? (2)

Answer 8

fractional distillation

cracking and reformation

Question 9

2d: Why are alkanes a good source of fuel? (2)

Answer 9

provide a lot of energy

we already have the methods and equipment

Question 10

2d: Why should we have alternative sources of fuel besides alkanes? (2)

Answer 10

non-renewable source (crude oil)

CO2 produced from combustion, affecting climate change

Question 11

2e: What are the products of combustion of a hydrocarbon? (2)

Answer 11

CO2, H2O

Question 12

2e: What is a free radical?

Answer 12

an unstable molecule

Question 13

2e: Name the stages of free radical substitution. (3)

Answer 13

initiation
propagation
termination

Question 14

2e: Describe the initiation stage of free radical substitution (halogen + alkane).

Answer 14

one C-H bond splits, making the hydrocarbon a radical (e.g. CH3CH3 -> CH3CH2. + H.)

Question 15

2e: Describe the propagation stage of free radical substitution (halogen + alkane).

Answer 15

one of the halogen atoms breaks off and joins onto the hydrocarbon radical (e.g. CH3CH2. + Cl2 -> CH3CH2Cl + Cl.)

Question 16

2e: Describe the termination stage of free radical substitution (halogen + alkane).

Answer 16

every radical joins with another radical until there is none left (e.g. Cl. + H. -> HCl)

Question 17

2e: How do you represent the movement of an electron when drawing the mechanism of a free radical reaction?

Answer 17

a single-headed curly arrow from the bond to an atom

Question 18

2e: Why does a free radical reaction have more products than expected?

Answer 18

the radicals can join onto any other radical, so for example the substitution of chlorine into ethane can also give butane and hydrogen as well as chloroethane and HCl

Question 19

3a: What is the general formula of alkenes?

Answer 19

CnH2n

Question 20

3a: What is an alkene?

Answer 20

an unsaturated hydrocarbon with one carbon-carbon double bond

Question 21

3a: Describe the structure of a double bond.

Answer 21

consists of a pi bond (single covalent bond between two sp3 orbitals) and a sigma bond (between two p orbitals; they bend to create arcs either side of the pi bond)

Question 22

3b: Describe cis-trans isomerism.

Answer 22

in a cis molecule, the heaviest groups (e.g. methyl, ethyl) are both on the same side of the double bond; they are opposite in a trans molecule

Question 23

3b: Why does cis-trans isomerism occur?

Answer 23

restrictive rotation (the C=C double bond cannot rotate)

Question 24

3c: Describe E-Z isomerism.

Answer 24

similar to cis-trans; comes into effect when atoms besides C and H are involved - E = opposite, Z = same - and is decided by atomic number

Question 25

3di: addition CnH2n + H2 -> | an alkene + hydrogen goes to... with catalyst...

Answer 25

CnH2n+2 | an alkane; catalyst Ni

Question 26

3dii: addition CnH2n + F2 -> | an alkene + halogen goes to...

Answer 26

CnH2nF2 | a di-sub halogenoalkane

Question 27

3diii: addition CnH2n + HCl -> | an alkene + hydrogen halide goes to...

Answer 27

CnH2n+1Cl | a mono-sub halogenoalkane

Question 28

3div: addition CnH2n + O2 -> | an alkene + oxygen goes to... with catalyst...

Answer 28

CnH2n(OH)2 | a diol; catalyst K2MnO4

Question 29

3ei: Identify and describe the mechanism of the reaction between HBr and C2H4

Answer 29

electrophilic addition HBr is polarised, so H end is pulled towards the double bond in ethene this takes out an electron, creating a Br. radical the H joins to the ethene, creating an ethyl radical eventually a Br. radical attaches to the ethyl

Question 30

3ei: Identify and describe the mechanism of the reaction between Br2 and C2H4

Answer 30

electrophilic addition Br2 becomes polarised near the double bond the delta+ end pulls an electron from the bond the Br-Br bond splits, creating a Br. radical and C2H4Br. radical these eventually join

Question 31

3eii: In one stage of an electrophilic addition reaction between H. and .CH2.CHCH2, where does the H. join on and why?

Answer 31

the one at the end; it is less stable as there are fewer nearby covalent bonds to provide stability

Question 32

3f: Describe the test for a C=C bond.

Answer 32

bromine water: orange -> colourless

Question 33

3f: What is the equation of the test for a C=C bond (using ethene an asn example)?

Answer 33

C2H4 + 1/2Br2 + OH -> C2H4BrOH

Question 34

3g: Describe the mechanism of addition polymerisation.

Answer 34

initiator Q-Q splits to give Q. Q. Q. interacts with CnH2n to split the double bond and create a .CnH2nQ radical this reacts with another CnH2n and so on to create a chain eventually the other Q. reacts with the end of the chain to finish the reaction