10: alkenes

The functional group contains a double covalent bond which is a

region of high electron density

The sheep around each carbon atom in the carbon carbon double bond is

trigonal planar bond angle 120°

pi bond

forms when p orbitals overlap

presence of a pi bond means there is

restricted rotation about the CC bond

two two or three carbon carbon bonds

diene, triene

Why does EZ isomerism occur

as a result of restricted rotation about the trigonal planar carbon carbon double pond

for an alkene to exhibit EZ isomerism

each carbon atom of the carbon carbon double bond must be bonded to different groups

to be the z isomer

both highest priority groups should be on the same side of the CC bond

highest priority

the atom with the highest atomic number

are alkenes reactive or unreactive and why

they are reactive due to the high electron density of the CC double bond

What kind of reactions do alkenes undergo in which a small molecule is added across the CC group to form a saturated molecule

addition reactions

electrophile

electron pair acceptor

Why do alkenes react with electrophiles

electrophiles are attracted to the high electron density in the carbon carbon double bond

What happens during the reaction

covalent bonds are both broken and formed producing a reactive positively charged intermediate called a carbocation

What is a mechanism

shows the breaking and forming of covalent bonds using curly arrows

curly arrows must be drawn accurately and start from either

a lone pair or a covalent bond

reagent of reaction of alkenes in halogens

X2

conditions

room temp

What is the electrophile in this reaction

the bromine molecule

What does the high electron density do to the BR2 molecule

it induces a dipole

how does the BRBr bondn break

by heterolytic fission

bromine is used

to test the presence of a CC group: orange to colourless

electrophilic addition of concentrated sulphuric acid to alkenes reagent and conditions

reagent: concentrated sulphuric acid
conditions: room temp

What does a sulphuric acid molecule look like

A person cheering

how do organic hydrogens sulfates form an alcohol

they are readily hydrolyzed with warm water

how can alcohols be prepared from alkenes

hydration of alkenes with steam in the presence of a phosphoric acid catalyst

primary carbocation

A carbocation which has one carbon atom directly bonded to the positively charged carbon. only one alkyl group

secondary carbocation

A carbocation which has two carbon atoms directly bonded to the positively charged carbon.

tertiary carbocation

A carbocation which has three carbon atoms directly bonded to the positively charged carbon.

Which is the most stable carbocation

tertiary

Which is the least stable carbocation

primary

positive inductive effect

The tendency of alkyl groups to release electrons which help to stableize the positive charge of carbocation

addition to an unsymmetrical alkene produces

two different organic products, the major product and the minor product

yield of a particular product is related to

stability of carbo cation formed from

explanation for why something is a major product

X is the major product - formed via a secondary carbocation. 2° carbocations have two alkyl groups. 1° carbo cations have only one alkyl group. 2 alkyl groups release more electrons and 2° carbo cations :. The more stable than 1°

when how hydrogen is added across a C=C bond a what is produced

an alkane

hydrogenation of alkanes is important because

it's an important industrial process for example margarine is produced by the hydrogenation of long chain fats or oils which contain CC double ones

how are polymers formed

when many is small molecules called monomers join together to form a very large molecule

alkenes act as monomers in

polymerization reactions- CC double bond breaks allowing monomers to add together

repeating unit

specific arrangement of atoms that occurs in the structure over and over again

polypropylene use

food containers

polyprop 2 enenitrile use

synthetic fibres which are used in blankets, rugs and clothing

polytetrafluoroethene use

Teflon - non-stick pans

polyphenylethene use (polystyrene)

low density so used for packaging

poly 1,1 dichlorothene use

shower curtains, plastic films

properties of poly alkenes

unreactive due to the backbone of single CC bonds so saturated

properties of poly alkenes depend on

the structure and the intermolecular forces between neighbouring polymer chains

polyethylene has

van der Waals between neighbouring chains

The properties of polymers like poly ethylene can be modified by

increasing branching

What is the effect of this

it decreases points of contact so the van der Waals forces are weakened which causes increased flexibility and a lower melting point

polychloroethane properties

rigid and brittle. contains polar CCL bonds therefore has permanent dipole dipole forces between polymer chains.

plasticisers

make polymer more flexible as they force neighbouring chains apart allowing them to slide over each other. get in between neighbouring chains and reduce intermolecular forces.