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Chem > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

What is the general formula of alkenes?

A

CnH2n

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2
Q

Structure of alkenes?

A

Bond is roughly 120°
Restricted density - Double bond cannot rotate like in alkanes, there is a p orbital on each carbon which overlap to from a cloud of electron density.

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3
Q

Types of alkene isomers?

A 
Position isomers - double bond in different position 
Geometrical isomers (stereoisomerism) - same structural formula, bonds arranged differently in space
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4
Q

What are the two types of geometric isomers?

A 
Z isomer (cis) two atoms of higher atomic number on same side 
E isomer ( trans) two atoms of higher atomic number on different side
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5
Q

Physical properties of alkenes?

A

not much different to alkenes as van der waal forces are the only intermolecular forces acting between alkene molecules. melting and boiling point increase w n° of carbons.

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6
Q

Are alkenes soluble in water?

A

no

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7
Q

How do alkenes react?

A

More reactive than alkenes, double bond between C’s forms electron rich area in the molecule that can be attacked by electrophiles ( electron pair acceptors)

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8
Q

What reactions do most alkenes go through?

A

Because they’re unsaturated- addition reactions like electrophilic additions

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9
Q

Do alkenes burn in air?

A

yes they take part in combustion

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10
Q

What must a molecule contain to be a geometric isomer?

A

A double bond

2 different groups attached on each carbon around the double bond

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11
Q

write the equation do burning ethene in the air?

A

C2H4 + 302-> 2H20 + 2CO2

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12
Q

How do you test for an alkene?

A

Bromine water is added to an alkene, it turns colourless.

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13
Q

What are alkenes

A

hydrocarbons - made of C and H only

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14
Q

Are alkenes saturated or unsaturated

A

unsaturated - there aid at least 1 Carbon bond

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15
Q

Why are alkenes reactive

A

The double bonds have high electron density

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16
Q

How do cycloalkenes differ from straight chained alkenes

A

Have 2 fewer Hydrogens

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17
Q

Why do electrophoresis attack alkenes

A

high density of electron in double bonds is attacked by electrophiles- these are added to the molecule

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18
Q

What is an electrophile

A

Electron pair acceptor , deficient in electrons so they are attracted to the double bond

19
Q

What are some examples of electrophiles

A 
NO2+
H+
H-Br
H2SO4
Br2
20
Q

What is the test for alkenes?

A

Add bromine water to an alkene, colour should change from brown/orange to colourless. Bromine ( brown/orange) is the electrophiles and adds to the alkene forming a dibromoalkane (colourless)

21
Q

How do alkenes form halogenoalkenes?

A

They react with hydrogen halides.

HBr is polarised , an electron pair in the double bond is attracted to the delta + hydrogen and forms a bond, which breaks the HBr bond, a carbocation intermediate is formed and Br- is attracted to C+, bromoethane is formed

22
Q

What happens when a hydrogen halide reacts with an unsymmetrical alkene?

A

2 different products are formed;

Major product and minor product

23
Q

What determines the amount of the 2 products formed?

A

The stability of the carbocation intermediate, the more alkyl groups it’s attached to the more stable it will be as more electrons are being pushed towards the positive carbocation.

24
Q

What are the types of carbocations, from least to most stable

A
  1. Primary Carbocation ( 1 alkyl group)
  2. Secondary CC (2)
  3. Tertiary CC (3)
25
Q

How do alkenes form alkyl hydrogen sulfates

A

React with COLD and CONCENTRATED H2SO4 sulfuric acid

26
Q

What does H2SO47 used as in a reaction

A

catalyst

27
Q

How do you make alcohol from an alkyl hydrogen sulfate

A

Adding COLD water to to your alkyl hydrogen sulfate will form an alcohol

and H2SO4 reformed - shows it’s a catalyst

28
Q

what is this process called?

A

Hydrolysis

29
Q

What are the monomers for Polymers

A

Alkenes

30
Q

What are the types of monomers?

A

Natural- proteins and natural rubbers

Synthetic - poly(ethane) and poly(propene)

31
Q

Are polyalkenes saturated or unsaturated?

A

Saturated

32
Q

What are polyakenes reactivity like?

A

Unreactive due to the fact they are non polar meaning they don’t degrade well in landfill

33
Q

What are the polyalkene properties?

A

Intermolecular forces dictate their properties, due to their non polarity they only have van der waal forces between them

34
Q

What does a longer polyalkene chain mean?

A

The longer the chain ( the bigger the SA) the closer they are, the more van der waal forces you have a higher melting point

35
Q

What does it mean when the polymer chains are shorter and have branching

A

They are more flexible and weaker

36
Q

What happens when polymers have no branching?

A

They are more rigid and stronger

37
Q

What happens when polyalkenes have halogens- like chlorine ( PVC - polyvinyl chloride)

A

They can form stronger permanent dipole dipole forces and so different properties- more strong and durable used for outdoor,lightweight and cheaper
as they have stronger forces

38
Q

Conditions of an alkene to polyalkene

A

addition polymerisation

low temperature high pressure

39
Q

conditions of alkene to bromoalkane

A

electrophilic addition
hydrogen halide
room temperature

40
Q

alkene to dibromoalkane

A

electrophilic addition
Br2
room temp

41
Q

alkene -> alkylhyrdogensulfate

A

electrophilic addition

reagent: Conc sulfuric acid
condition: cold

42
Q

akylhydrogensulfate->alcohol

A

hydrolysis
water
warm

43
Q

alkene-> alcohol

A

hydration:
Steam
300°,high p - 70atm , Catalyst - H3PO4 or H2SO4

44
Q

who’s rule was the addition of unsymmetrical electrophiles for

A

markovnikov

Chem (8 decks)

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