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A - Level Chemistry > Chapter 13 > Flashcards

Chapter 13 Flashcards

1
Q

Are alkenes unsaturated or saturated

A

Unsaturated

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2
Q

General formula of alkenes

A

CnH2n

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3
Q

What’s the bonding like for each of the C of C=C in alkenes

A

3 of 4 electrons used in 3 sigma bonds ( 1 to other C atom of C=C & other 2 electrons to other atoms)

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4
Q

What happens to 4th electron in each C of C=C in alkenes

A

1 electron (in p-orbital) on each C of C=C not involved in sigma bonds

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5
Q

Define pi bond

A

Sideways overlap of 2 p-orbitals, 1 from each C of C=C

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6
Q

Where is pi electron density concentrated in an alkene

A

Pi electron density concentrated above and below line joining nuclei of bonding atoms

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7
Q

Shape and bond angle in alkene

A

Trigonal planar

120*

3 regions of electron density around each of C atoms
- 3 regions repel each other as far apart as possible
- all of atoms are in same plane

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8
Q

Define stereoisomer

A

Compounds with same structural formula but with different arrangent of atoms in space

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9
Q

Conditions needed for E/Z isomerism

A

C=C

Diff groups attached to each C of C=C

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10
Q

Z isomer

A

Groups of higher priority on same side of C=C

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11
Q

E isomer

A

Groups of higher priority are diagonally opposite across C=C

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12
Q

What is the Cahn-Ingold-Prelog rule

A

Atoms attached to each C atom in C=C are given priority based on their atomic number

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13
Q

When can Cis-trans isomerism only be used

A

When each C atom in C=C is attached to a single H atom

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14
Q

Why’s there stereoisomerism around C=C

A

Rotation about C=C restricted, groups attached to each C fixed relative to each other

Reason fro rigidly - position of pi-bond electron density above + below plane of sigma bonds

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15
Q

2 types of isomerism

A

E/Z isomerism

Optical isomerism

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16
Q

Conditions needed for Cis-trans isomerism

A

C=C

1 of attached groups on each C of C=C must be the same

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17
Q

How to assign priority if 2 atoms attached to C=C are same

A

Find 1st point of difference

Group with higher atomic number at 1st point of difference is given higher priority

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18
Q

use enthalpy data explain why pi bonds break more readily than sigma bonds

A

In Ethene:

C-C (sigma bond) has BE = 347 kJ mol-1

C=C (pi and sigma) BE = 612 kJ mol-1

BE of pi bond : 612 - 347 = 265 kJ mol-1

Pi bonds weaker than sigma bond, so is broken more easily due to lower BE

19
Q

Hydrogenation of alkene

A

Hydrogen

Ni at 423K

Form alkane

20
Q

Are alkenes more/less reactive than alkanes

A

More reactive

21
Q

Why are alkenes reactive

A

C=C made of sigma + pi bonds

Pi electron density conc above + below plane of sigma bond

Pi electrons outside of C=C —> so are more exposed than electrons in sigma bond

Pi bond breaks readily & undergo addition reactions easily

22
Q

Hydration of alkenes

A

Steam/H2O(g)

H3PO4

Form alcohol

23
Q

Reaction of alkene with hydrogen halide

A

Hydrogen halide (g)

Room temp

Form haloalkane

24
Q

Test for unsaturation

A

Br2

Colour change = orange to colourless (bromine water decolourises)

25
Q

Halogenation of alkenes

A

Room temp

Br2/Cl2

Form haloalkane

26
Q

Type of bond fission in electrophilic addition

A

Heterolytic fission

27
Q

What’s the most stable carbocation

A

Tertiary carbocation

( stability increases from primary to tertiary carbocation)

28
Q

Explanation for electrophilic addition of but-2-ene with HBr

A

(Delta neg) Br more EN than H (delta pos)

Electron pair in pi bond attracted to delta pos H

C=C break

Bond form between H of HBr and C of C=C

H-Br break by heterolytic fission, electron pair go to Br

Br- and carbocation form

Br- react with carbocation to form addition product

29
Q

Explanation of Br2 and propene

A

Pi electrons interact with electrons in Br2

Induces dipole on Br-Br

Electron pairs in pi-bond attracted to delta pos Br, cause C=C to break

Bond form between C and Br

Br-Br break by heterolytic fission, electron pair for to delta neg Br

Br- and carbocation form

Br- react with carbocation to form product

30
Q

define ectrophile

A

Atom/group of atoms that’s attracted to a electron rich centre & accepts an electron pair

31
Q

Markownikoffs rule

A

When a H-halide reacts with an unsymmetrical alkene the H of H-halide attaches itself to C of alkene with greater number of H atoms and smaller number of C atoms

32
Q

Why’s tertiary carbocation most stable

A

carbocation stability linked to e^- donating ability of alkyl groups

each alkyl group donates + pushes e^-s towards pos charge of carbocation

pos charge spread over alkyl groups

more alkyl groups attached to pos-Charged C atom, more charge is spread out,making ion more stable

33
Q

What’s the major product

A

more stable carbocation

34
Q

Using wast polymer as fuel

A

some polymers made from natural gas and hard to recycle, they have high energy store

incinerate waste polymer, produce heat, generate steam, drive turbine producing elelctrcity

35
Q

Pros of polymers

A

Readily available

Cheap

Convenient for throwaway society

Lack reactivity - suitable for storing food

36
Q

Cons of polymers

A

Lack reactivity

Enviro effect - killing marine life

37
Q

Bioplastics

A

produced from plant starch, cellulose, plant oils, and proteins offer a renewable and sustainable alternative to oil-based products

  • protects enviro and conserves valuable oil refineries
38
Q

PVC recycling

A

disposing PVC is hazardous due to high Cl content and additives it contains

  • when burnt releases Hydrogen chloride (corrosive gas) and pollutants
39
Q

Compostable polymers

A

degrade and leave no visible/toxic residues

  • based on poly(lactic acid) becoming more common
40
Q

photodegradable polymers

A

polymers that contain bonds that are weakened by absorbing light to start the degradation.

alternatively, light absorbing additives are used

41
Q

Feedstock recycling

A

chemical and thermal processes that can reclaim monomers, gases or oil from waste products

  • products made from this resemble the ones made from crude oil, so can be used as raw materials for production of new polymers
  • advantage = can handle unsorted and unwashed polymers
42
Q

Recycling polymers

A

pros:
- reduce enviro impact
- conserve finite fossil fuels
- decrease waste going to landfill

.cons:
- if polymer is mixed, it renders the product unusable so it can’t be reused

43
Q

Biodegradable polymers

A
  • broken down by microorganisms into H20, CO2 and biological compounds
  • made from starch/cellulose or contain additives that alter structure of traditional polymers so microorganisms can break them down.

A - Level Chemistry (11 decks)

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