Alkenes Flashcards

1
Q

What are alkenes?

A

Unsaturated hydrocarbons

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2
Q

State what is meant by the term electrophile

A

An electron pair acceptor

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3
Q

Name the reaction that occurs when an alkene is turned into an alkane (eg C2H4 + HBr – > C2H5Br)

A

Electrophilic addition

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4
Q

Describe and explain the electrophilic addition of HBr to C2H4

A
The HBr molecule = polar (Br = more electronegative) --> H = electrophile
C=C makes this area v. negative
Opposites attract - electrophile attracted to double bond
However, Br slightly -ve, so is repelled and breaks off - takes the electrons
The electrophile (H) accepts electrons from a C and bonds --> other C now +ve (carbocation)
Carbocation attracts -ve Br - bonds
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5
Q

Why are major and minor products formed?

A

Some carbocations are more stable and so are more likely to be formed, more likely to hang around and bond with Nu (and vice versa)

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6
Q

What is a tertiary carbocation?

A

A C with 3 C groups around

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7
Q

State the stability of carbocations from least stable to most stable

A

methyl, primary, secondary, tertiary

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8
Q

What is the positive inductive effect?

A

Alkyl groups push electrons away from themselves towards C+

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9
Q

Why can electrophilic addition by Br2 occur?

A

High electron density repels the electrons in the Br2 as it nears, inducing a dipole

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10
Q

Electrophilic addition of what allows sulfuric acid to be reformed? What is the other product?

A

H2O (so hydrolysis reaction) to alkyl hydrogen sulfates

An alcohol is also produced

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11
Q

State what is meant by a polymer

A

Long chain molecule made from lots of small molecules joined together

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12
Q

State what is meant by a monomer

A

Small molecules that join together to make polymers

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13
Q

State what is meant by addition polymerisation

A

Formation of long chain molecules from lots of small molecules together with no other products

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14
Q

What are the conditions for addition polymerisation?

A

Pressure, high temperature, catalyst

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15
Q

Describe and explain addition polymerisation

A

Addition of something causes the double bond to break
1C is happy, but now 1 is missing a bond, so ‘steals’ one from the next molecule (causing that double bond to break)
Though this C is now happy, the 1C is not and is missing a bond and so ‘steals’ one from the next molecule, bonding with it…and so on

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16
Q

Plastics are not biodegradable. This means what?

A

They cannot be broken down by enzymes, acids or alkalis

17
Q

Why are plastics non-biodegradable?

A

To break down poly(alkanes) you have to break a non-polar C-C bond. Most bonds are broken down because they are polar or by hydrolysis (polar molecule itself)

18
Q

What is a plasticiser?

A

A small molecule that gets between the polymer chains, allowing them to slide past each other. This makes them more flexible

19
Q

State the meaning of the term stereoisomers

A

Same molecular and structural formula but different spatial arrangement

20
Q

A chemical test can be used to distinguish between saturated and unsaturated compounds. State the reagent, and what you would observe with each

A

Bromine
Saturated - stays orange
Unsaturated - Turns colourless

21
Q

The formation of ethanol from ethene uses conc. H2SO4 and proceeds in 2 stages.
S1 C2H4 + H2SO4 –> C2H5OsO2OH
S2 C2H5OSO2OH + H2O –> H2SO4 + C2H5OH
State the overall role of sulfuric acid in this process

A

It acts as a catalyst

22
Q

What are some typical uses of PVC poly(chloroethene)?

A

Depending on the type of PVC, can be used in underground pipes, or packaging