alkenes

What does unsaturated mean?

containing at least one carbon carbon double or triple bond

are alkenes saturated or unsaturated? what does this mean?

unsaturated - allowing them to react more easily than alkanes

what is a sigma bond

a bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons and with the electron density centred around line directly between the nuclei of the two atoms

what is a pi bond

a bond formed by the sideways overlap of two p orbitals, with the electron density above and below the plane of the bonding atoms

what is a double bond

one sigma bond and one pi bond

what is stereoisomerism

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

why does stereoisomerism happen in alkenes

because the c=c double bond cant rotate due to the pi bond

what is E/Z isomerism

a type of stereoisomerism which different groups attached to each carbon on a carbon=carbon double bond may be arranged differently in space due to the redistricted rotation of the c=c bond

what is cis trans isomerism

a special type of stereoisomerism

what are the cahn infold prolog naming rules

-describes which groups count most when assigning e or z

1. look at the group directly attached to each C of C=C
   2.the atom with the highest atomic number gets priority
2. if they are equal move on to the next atom along the chain
3. compare the highest priority group on each carbon

when is it a z isomer and when is it an E isomer

z - on ze zame zide
e- different sides

when do you use E/Z isomers

-when it has a c=c double bond
-when there are different groups attached to each carbon atom on the double bond

when in an alkene will there not be E/Z isomerism

when it is symmetrical

what is average bond enthalpy

the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecule of a gaseous species

is the bond enthaphy for a pi bond or a sigma bond higher and what does this mean

the pi bond is weaker than the sigma bond so it has a lower average bond enthaphy and is more easier broken

what does the fact that the bond enthalpy of a double c=c bond is not the same as the bond enthalpy of two sigma bonds mean

it shows that there are two distinct reactions in a double bond - it has a stronger sigma bond and a weaker pi bond

what reacts with an alkene during hydrogenation

hydrogen

what are the reaction conditions needed for hydrogenation

nickel catalyst and 150 degrees celsius

what are the visible changes of a hydrogenation reaction

there are no visible changes as hydrogen gas is absorbed

when drawing out a hydrogenation reaction what happens

the carbon carbon double bond breaks and an extra two hydrogens are added

what reacts with an alkesne design halogenation

a diatomic halide

what are the reaction conditions for halogenation

-room temp
-no uv
-usally bromine water

what are the observations of a halogenation reaction

orange bromine water turns colourless

what reacts with an alkene during hydration

water - in the form of steam

what are the reaction conditions for a hydration reaction

-phosphoric acid catalyst
-300 degrees celsius
-high pressure (60-70 atm)

what are the two observations for a hydration reaction

-no visable change

what is formed during a hydration reaction

an alchohol

what is electrophilic addition

an alkene addition reaction that formes saturated compounds

what does the double bond in an alkene represent? what does this mean?

-a double bon din an alkene represents a region of high electron density. this attracts electrophiles

what is an electrophile

ana electrophile is an atom or a group of atoms that is attached to an electron rich centre and accepts an electron pair

what is the reaction mechnqims for the electrophilic assitiomn of but-2-ene and HBr

-bromien is more electronegative than hydrogen so hydrogen bromine is polar
-the electron pair in the pi bond is attracted to the partially positive hydrogen atom, causing the double bond to break
-a bond forms between the hydrogen atom of the H-Br molecule and a carbon atom that was apart of the double bond
-the H-Br bond breaks by heterolytic fission, with the electron pair going to the bromine atom
-a bromie ion and a carbocation are formed
-the Br- ion reacts with the carbocation to from the addition product

what is a carbocation

An organic ion containing a positively charged carbon atom

what is addition polymerisation

a reaction in which may small unsaturated molecules (monomers) join together to form a polymer

when does Addison polymerisation occur

when the c=c double bond in each monomer breaks, following the molecule to link together without the formation of by products

draw out monomer and polymer for ethene

what are the three environmental concerns of polymers

disposing of waste products, recycling, pvc recyling

how is the disposal of waste polymers and environmental concern

-due to their lack of reactivity it prevents disposal challenges (non biodegradable)
-they are a serious environmental threat e.g marine life
-readily available sp used everywhere

how is PVC an environmental concern

-hazardous as there are high chlorine content and additive
-when burnt corrosive gas and pollurtents released
-can have solvent dissolve polymer

why are recycling alkenes hard

have to be sorted by type aand chopped into flakes, washed, dried, melted, pellets, new product

what are the two possible solutions for environmental concerns of polymers

using as fuel, feedstock recycling

how can polymers be used as fuels

-they are deprived from petroleum so they have a high energy store.
-incinerated - heat - steam - turbine - generator
-works for non recyclable

how does feedstock recycling work

-chemical and thermal process - reclaims monomers
-products are made to r

conditons for electrophilic addition

happens at room temp

What is Markownikoff's rule?

In electrophilic addition to alkenes, the major product is formed via the more stable carbocation

MAJOR AND MIINOE