alkenes
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general formula of alkenes
CnH2n
how do pi bonds form
sideways double overlap of 2p orbitals above and below the plane
what is the shape of alkenes?
trigonal planar
what is the bond angle of alkenes?
120
stereoisomers definition
same structural formula but a different arrangement of the atoms in space
what are the 2 types of stereoisomers
• E/Z isomerism - optical isomerism
explain how E/Z isomers occur
• restricted rotation around the double bond • groups attached are fixed relative to each other • rigid due to high electron density
what are the conditions needed for E/Z isomerism
• C=C double bond - different groups attached to each carbon atom of the double bond
what is cis- trans isomerism
used to describe a special case of E/Z isomerism
what are the conditions needed for cis- trans isomers?
• C=C double bond • more than 2 different groups attached to each carbon atoms of the double bond • one of the attached groups on each carbon must be a hydrogen
what is a cis- isomer called in E/Z isomerism?
z
what is a trans- isomer called in E/Z isomerism?
E
how are groups prioritised in Cahn- Ingold- Prelog?
• priority bases on their atomic number - the group with higher atomic number at the 1st point of difference has higher priority
explain why alkenes are more reactive than alkanes
• pi bonds are more exposed than sigma electrons - pi bonds readily break and alkenes undergo addition reactions easily
electrophile definition
electron pair acceptor
what is the characteristic mechanism for alkenes
electrophilic addition
why is the tertiary carbocation more stable than the secondary and primary carbocation?
• each alkyl group donates and pushes electrons towards the positive charge of the carbocation • the more alkyl groups attached to the positively charged carbon atom, the more the change is spread out, making it more stable
how are carbocations classified
classified by the number of alkyl groups attached to the positively charged carbon atom
what do feedstock recycling describe?
describes the chemical and thermal processes that can reclaim monomers, gases, or oil from waste polymers
state 1 atmospheric pollutant caused by the burning of PVC
HCl(g)
how are polymers suitable for storing food and chemical safety?
lack of reactivity
what does recycling reduce?
reduces their environmental impact by conserving finite fossil fuels as decreasing the amount of waste going to landfill
what are the advantages of bio plastics?
• protect our environment - conserves valuable oil reserves
what is the advantage of feedstock recycling?
able to handle unsorted and unwashed polymers