Chapter 13: Alkenes

Alkenes are .............. hydrocarbons with a .......... ...........bond

unsaturated, double covalent C=C

formula for an alkene

CnH2n

Alkenes contain a .......... bond and a ........ bond between 2 Cs

sigma, pie

sigma bond/σ bond

-a ........ ..........bond

- electrons move .............. ..... ......... between atoms

-involves overlap of 2 .............

-1 ............... is given from each .......... atom

-single covalent, C-C

-directly in line

-orbitals

-electron, bonding

pi bond/ π bond:

- and sigma bond together form a ......... .......... bond

- ........... move above and below the ............. of the atom

-involve overlap of 1 .... orbital on each ..........

-Each carbon contributes 1 ...... to the pair that's ......... in the pi bond

-double covalent C=C

-electrons, plane

-p, carbon

- electron, shared

π bond + σ bond forms..

a double bond between 2 Cs

single bonds are

sigma bonds

The shape around each C in an alkene is ............. .............. (bond angle .....)

trigonal planar, 120 degrees

π bond vs σ bond (where they are)

-π bond in a double bond

- σ bond in single and double bonds

π bond vs σ bond (where electrons move)

-π bond: above and below plane of atom

- σ bond: directly in line between atoms

alkanes vs alkenes:

-type of bonds involved...

-shape...

-bond angle...

-formula

-alkanes: sigma, alkenes: pi and sigma bonds

-alkanes: tetrahedral, alkenes: trigonal planar

-alkanes: 109.5 degrees, alkenes: 120 degrees

-alkanes: CnH2n+2, alkenes: CnH2n

In alkenes, the atoms around the .......... ....... bond can't move as there's no ........ ................. around it

double C, free rotation

stereoisomers: isomers with same ............. ............. but different ............... of atoms in space

-structural formula, arrangement

2 types of stereoisomers

E and Z

E/Z isomers:

-only occur in molecules with ......... bond

-groups attached to the Cs in C=C are in ............. positions

because of ...... electrons ............... & ............. the plane of the ..... bond

C=C

-fixed, pi, above, below, sigma

Z in E/Z stands for ................., so groups are on ............ sides of the molecule

zusammen, same

A molecule has an E/Z isomer if it has both:

-a ............ ............. bond

-.............. groups attached to each ..... of the C=C bond

-C=C double bond

-different, carbon

to decide if something is an E or Z isomer, find the highest priority atom:

-highest priority atoms have a ............. atomic number

higher

H H

\ /

C=C

/ \

CH3 CH3

name this molecule: (E or Z isomer and why)

Z-but-2-ene

as CH3 groups on same sides of the molecule

H CH3

\ /

C = C

/ \

CH3 H

name this molecule: (E or Z isomer and why)

E-but-2-ene

as CH3 groups on different sides of molecule

H CH3

\ /

C = C

/ \

Cl OH

-highest priority groups are ...

-this molecule is called..

-Cl and O

-Z-1-chloro, 2-hydroxy prop-1-ene

H3C CH2CH2Cl

\ /

C = C

/ \

H CH2CH2OH

name this molecule:

Z-3-chloro ethyl 1-hydroxy pent-3-ene

Cahn-Ingold-Prelog Nomenclature:

-system used to name ..... ............ based on priority of groups attached to ........

-Higher ......... ......... is priority

-E/Z isomers, C=C

-atomic number

cis/trans isomers:

-special case of ...... isomers

-one attached group on each C of the C=C must be a .....

-E/Z

-hydrogen

Cis isomers: H atoms on ............. side

-always ......... isomers

same, z

Trans isomers: H atoms on ............. side

-always ....... isomers

-opposite/different, E

CH3 CH3

\ /

C = C

/ \

H H

name this cis/trans isomer

cis but-2-ene

CH3 H

\ /

C = C

/ \

H CH3

name this cis/trans isomer

trans but-2-ene

alkenes are ......... reactive than alkanes, due to the presence of a ..... bond

-more, pi

Reactivity of alkenes:

-the presence of a pi bond makes them ........... reactive than alkenes because the pi e- ........... & ........... the plane are more ............ than e- in the sigma bond

-therefore, pi bonds break .......... easily than sigma bonds

-more, above, below, exposed

-more

Alkenes are involves in ......... reactions ( as it ........ the C=C bond)

addition, breaks

bond enthalpy for σ > π

because...

more energy needed to break a sigma bond than a pi bond

which is more reactive, alkenes or alkanes? and why?

alkenes

e- in pi bond above and below plane of atom are more exposed than e- in sigma bonds

Alkene + hydrogen (with ......... catalyst) -->

(nickel catalyst) --> alkane

alkene + halogen-->

(this is used as a test for ........ e.g. bromine water)

haloalkane, unsaturation

alkene + hydrogen halides --> ........

what happens if the alkene is unsymmetrical?)

haloalkane

(2 possible products if alkene unsymmetrical)

alkene + steam --> (with conc. ........... catalyst)

if alkene unsymmetrical: 2 possible .........

alcohol (H2SO4 catalyst)

-products

electrophile

atom/group of atoms that's attracted to an electron rich centre & accepts an electron pair

electrophilic addition:

-........... take part in addition reactions

-........ reactants, ............ product

-electrophilic addition is a .............

-the high density of ..... e- attracts .........

-alkenes

-2,1

-mechanism

-pi, electrophiles

draw mechanism for ethene + HBr

ethene + HBr

-the bond breaks h........ly

-the intermediate is a c......

-this mechanism is called ......... ........

-HBr already has a d....... because Br is more ........ than H

-the electrophile is ...

-heterolytically

-carbocation

-electrophilic addition

-dipole, electronegative

-Hδ+ in HBr

draw mechanism for ethene + Br2

with 2 dots on Br-

-bromine isn't ........., but can react with alkenes because the ..... bond electrons repel electrons on one ......

-this is an i......... .........

polar, pi, Br, induced dipole

when propane reacts with HBr, why is 2-bromopropane formed more than 1-bromo propane?

2-bromo propane has a slightly more stable intermediate

-Cs surrounding the carbocation funnel e- to it

-therefore it's the major reaction

Markovnikoff's Rule

the H in a hydrogen halide attaches itself to the C of the alkene with the most Hs and least Cs

Electrophilic addition occurs in 2 steps:

step 1 called c.........

-a ............ intermediate is formed (fyi these can be primary or secondary)

carbonation, carbocation

carbocations:

-become more stable, the more .......... groups are joined to the ..... ion

-the more stable route produces the ....... product

alkly, carbon, major

draw primary, secondary & tertiary carbocations

(using R group)

addition polymerisation:

-u........ alkene m........ join to form long s....... c..... aka p..........

unsaturated monomers, saturated chains, polymers

industrial polymerisation conditions:

-high ....

-high .....

-a ........

temp, pressure, catalyst

polymers have high m......... m...

molecular mass

repeat unit is

the specific arrangement of atoms in the polymer molecule that repeats

repeat unit is always drawn with ...

square brackets, n after bracket

A B

I I

n[ C=C ] -->

I I

D E

draw polymer repeat unit

A B

I I

-[- C-C-]-

I I

D E n

waste polymers can be: (3)

-r.......

-used as f........

-used as f.... to...

recycled, feedstock, fuel, generate energy

environmental concerns:

-many alkene based polymers aren't .........

biodegradable

polymers are used because they're:

-c..... & available

-lack of r........... (makes them suitable to store food)

cheap, reactivity

recycling polymers:

-reduced ...... impact by conserving f........ f..... f..... & decreasing l..... w........

environmental, finite, fossil, fuels, land waste

recycling polymers:

-polymers must be sorted by t.....

-they're ch.., w.....,d.. & m......(verbs)

type, chopped, washed, dried, melted

PVC recycling:

-is h......... due to high c....... content & range of a........

hazardous, Chlorine, additives

PVC recycling:

-PVC isn't suitable for l......

-when burnt it releases h.......... c......... which is a c... g.....

landfill, hydrogen chloride, corrosive gas

PVC recycling:

-s......... are used to d.......... PVC & high-g..... PVS is recovered by p........

solvents, dissolve, grade, precipitation

Waste polymers as fuel:

-polymers derived from p........... or natural g...... have high stored e..... value

petroleum, gas, energy

Waste polymers as fuel:

-polymers can be i....... making heat/s...... to drive t...... producing e.............

incinerated, steam, turbines, electricity

feedstock recycling:

-describes c........./t........ processes that reclaim m........, gases & oils from waste polymers

chemical, thermal, monomers

feedstock recycling can handle un......... polymers

washed/sorted

bioplastics:

-produced from plant s.....

-offer a r......... alternative to o....-based products

starch, renewable, oil

biodegradable polymers:

-broken down by m....... into biological compounds

microorganisms

compostable polymers:

-de..... and leave no visible/toxic r.......

degrade, residue

photodegradable polymers

Contain bonds that are weakened by absorbing light to start the degradation