Chapter 14 - Alkenes Flashcards

1
Q

general formula of an akene

A

CnH2n

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2
Q

general formula of a cyclic alkene

A

CnH2n-2

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3
Q

why are alkenes more reactive than alkanes

A

because they have a region of high electron density (the double bond) which allows them to undergo addition reactions by attracting electrophiles

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4
Q

whats an electrophile

A

electron pair acceptor

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5
Q

another name for double bond

A

pi bond

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6
Q

outline addition reactions with halogens (Br2)

A

Step 1 - The high electron density of the C=C double bond repels electrons in the bromine molecule, polarising the Br-Br bond.
Step 2 - This leads to heterolytic fission of the Br-Br bond, with one bromine atom taking the bonding pair of electrons, creating a positively charged bromine which bonds to one of the carbon atoms.
Step 3 - A positively charged carbocation intermediate forms. The negatively charged bromide ion then bonds to the other carbon atom.
Step 4 - The final product, 1,2-dibromoethane, has a bromine atom bonded to each of the original alkene carbon atoms.

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7
Q

whats a carbocation

A

when a carbon atom is positively charged in a molecule

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8
Q

test for alkenes

A

decolorizes bromine water due to addition reaction with alkene

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9
Q

what conditions are used when hydrating alkenes to form alcohols

A

phosphoric acid
300 degrees Celsius
60 - 70 atm

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10
Q

what are primary secondary and tertiary carbocations

A

primary have one alkyl group attached, secondary have 2 and so on

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11
Q

why does the stability of carbocations increase with more alkyl groups

A

alkyl groups have a tendency to release electrons or a “positive inductive effect” which stabilizes the positive charge

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12
Q

what are major and minor products in electrophilic addtion

A

major product is made the most, it results from a more stable carbocation bonded to the thing

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13
Q

how can you get an alcohol from the products of an electrophilic addition reaction with sulfuric acid

A

Water and heat hydrolyse the alkyl hydrogen sulfate back to alcohols and sulfuric acid.

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14
Q

whats a polymer
whats a monomer

A

monomer is one unit of a polymer
polymer is long chain of monomers

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15
Q

why are alkenes used to make plymers

A

the C=C bond breaks to allow alkenes to join up and form a carbon chain

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16
Q

what process is joining together mnay monomers by breaking the C=C bond

A

addtion polymerisation

17
Q

hwo does chain length affect physical properties of a plymer

A

Longer chains allow more surface contact between neighbouring chains. This strengthens the intermolecular forces.

18
Q

hwo do branches affect physical properties of a plymer

A

Straight chains can pack together closely in an ordered structure, maximising intermolecular forces. Highly branched chains cannot pack as efficiently, reducing contact between chains.

19
Q

what are plasticisers

A

plasticisers are small molecules that can be added to polymers to increase flexibility

20
Q

how do plasticisers work

A

Plasticiser molecules position themselves between polymer chains.
This pushes the chains apart, weakening intermolecular forces between polymer chains.
The chains can now slide over each other more easily when bent.

21
Q

why are addtion polymers unreactive

A

Polyalkenes contain only single covalent bonds. This makes them saturated compounds with maximum stability.
They also have a carbon backbone lacking any polar groups, giving an overall non-polar molecule.