alkenes & alkanes

Question 1

what is a sigma bond?

Answer 1

single bonds which involves the direct overlap of orbitals in alkenes
can rotate freely and stronger bond than pi

Question 2

what is a pi bond?

Answer 2

double bonds which involves the sideways overlap of two orbitals.
consists of one sigma bond and one pi bond
cannot rotate freely

Question 3

2 effects of pi bond

Answer 3

1. restricts rotation of double bond
2. high electron density

Question 4

symmetrical alkenes

Answer 4

same groups on both sides

Question 5

asymmetrical alkenes

Answer 5

do not have the same groups at each end of the double bond

Question 6

what is the shape and bond angle for C-C and C-H bonds in alkanes?

Answer 6

109.5 & tetrahedral shape
minimises the repulsion between shared pair of electrons

Question 7

what is the shape and bond angle for C=C in alkenes?

Answer 7

120 & trigonal planar shape
any additional carbons will have a bond angle of 109.5 - only the double bond flattens out.

Question 8

general formula of alkenes

Answer 8

CnH2n

Question 9

general formula of alkanes

Answer 9

CnH2n+2

Question 10

explain bond length and strengths in alkanes, alkenes and benzenes

Answer 10

alkane - longest bond length however has the weakest

Question 11

alkene + halogen = ?
conditions?

Answer 11

halogenoalkane
no conditions needed

Question 12

alkene + hydrogen halide = ?
conditions?

Answer 12

halogenoalkane
no conditions needed

Question 13

alkene + hydrogen = ?
conditions?

Answer 13

alkane
nickel catalyst and heated to 150

Question 14

alkene + water = ?
conditions?

Answer 14

alcohol
H3PO4, 300 degrees and 60 -70 atmospheric pressure atm

Question 15

alkene + sulphuric acid = ?
conditions?

Answer 15

alkyl hydrogen sulphate
no conditions needed

Question 16

electrophiles

Answer 16

species that accept a pair of electrons and attracted to high electron density

Question 17

describe electrophilic addition with halogens and alkenes

Answer 17

C=C has high electron density and 4 electrons are shared between atoms
electrons are negatively charged which makes alkenes attracted to electrophiles
area of high electron density polarises non polar halogen molecule to make it an electrophile
double bond is broken and new groups are added to both carbons on either side of C=C

Question 18

what can stability carbocations determine

Answer 18

which product is more likely to be made & which carbocation is formed from an asymmetrical alkene and hydrogen halide

Question 19

what are the two factors that determine which carbocation is formed?

Answer 19

where the double bond is and whether there are branches

Question 20

describe the trend of stability from tertiary to primary carbocations

Answer 20

stability decreases from tertiary to secondary to primary

Question 21

define stereoisomers

Answer 21

compounds with the same structural formula but their atoms have a different arrangement in space

Question 22

isomers

Answer 22

molecules with the same molecular formula but different arrangement of atoms