alkenes

Question 1

why is there no rotation around the C=C double bond?

Answer 1

due to pi orbital
electron density above + below single bond
holds the C atoms in place

Question 2

why are alkenes more reactive than alkanes?

Answer 2

higher electron density of double bond

pi bond is easier to break

Question 3

what IM forces of attraction do alkenes have?

Answer 3

only vdW due to non-polar bonds

Question 4

why are alkenes not soluble in water?

Answer 4

non polar bonds

van der waals are weaker than H bonding

Question 5

what is an electrophile?

Answer 5

electron deficient atom/ion
accept a pair of electrons
(from the c=c bond)

Question 6

what is the most stable kind of carbocation intermediate?

Answer 6

alkyl groups
have positive inductive effect
so most stable carbocation is the one BONDED TO MOST OTHER C ATOMS
(tertiary)

Question 7

major products will be formed from which type of carbocations?

Answer 7

tertiary

(or most stable available?

Question 8

conditions needed for electrophilic addition of H2O to an alkene?

Answer 8

acid catalyst

phosphoric acid usually

Question 9

conditions needed for electrophilic addition of a hydrogen halide to an alkene?

Answer 9

room temperature

Question 10

conditions needed for electrophilic addition of halogen molecule to an alkene?

Answer 10

room temperature

organic solvent

Question 11

how does a non polar molecule act as if it were an electrophile?

Answer 11

C=C has high electron density
induces a temporary dipole in halogen molecule
partially positive atom attracted to double bond

Question 12

3 uses of poly(chloroethene) / PVC

Answer 12

drainpipes
vinyl
aprons

Question 13

why do things containing mainly c-c and c-h bonds not decompose easily?

Answer 13

bonds are non polar

so not attacked by enzymes

Question 14

what are stereoisomers?

Answer 14

molecules with same structural formula
BUT
different spatial arrangement of atoms/gps

Question 15

what type of bond is the C=C bond?

Answer 15

planar bond

Question 16

what is addition polymerisation?

Answer 16

reaction by which alkenes react with another alkene to form polymers

Question 17

why are addition polymers unreactive?

Answer 17

lack reaction C=C bond
this is an area of high electron density
and vulnerable to electrophilic attack

Question 18

forces between polymer molecules?

Answer 18

weak vdW forces

Question 19

why do some polymers melt over a range of temperatures?

Answer 19

consist of chains of different lengths

varying strength of vdW

Question 20

why are the IM forces between polymers often strong?

Answer 20

chains often long
many electrons
many vdW

Question 21

why does a tertiary carbocation form the major product?

Answer 21

tertiary carbocation has more alkyl gps attached 
POSITIVE INDUCTIVE EFFECT 
reduce + charge on carbon 
MORE STABLE 
remains in reaction mixture longer 
so 
MORE LIKELY TO REACT WITH ELECTROPHILE

Question 22

what is an electrophile?

Answer 22

electron pair acceptor

Question 23

what is a carbocation?

Answer 23

species containing positive charge on C atom

Question 24

is dilute sulphuric acid an electrophile?

Answer 24

NO

concentrated sulphuric acid is an electrophile

Question 25

what is heterolytic fission?

Answer 25

covalent bond breaks and both electrons move to one atom

2 OPPOSITELY CHARGED IONS FORMED