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AS Chemistry unit 2 > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

General formula for alkenes

A

CnH2n

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2
Q

Describe the method for nomenclature of alkenes

A
  1. Suffix of ene
  2. Find longest C chain containing double bond
  3. To describe position of c=c use lowest number
  4. If more than one C=C add ‘a’ to prefix and use ‘diene’ or ‘triene’ etc
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3
Q

Definition of unsaturated hydrocarbon

A

Contains at least one C=C or C(triplebond)C bond and is made of hydrogen and carbon only

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4
Q

Name the types of isomerism in alkenes

A
  1. Chain- different C chains
  2. Positional- position of C=C
  3. Geometric
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5
Q

Definition of geometric isomers

A

Molecule with the same structural formula, but a different arrangement of atoms due to the presence of one or more C=C bonds

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6
Q

How do geometric isomers occur?

A
  • Energy barrier to rotation about the C=C bond
  • each C=C bond must have two diff groups attached
  • categorised as ‘E-‘ and ‘Z-‘
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7
Q

How to classify E-Z molecules

A
  1. Split vertically
  2. On each side label the atom with the highest atomic number
  3. Split horizontally
  4. Same (zame) side ➡️ Z isomers
    Opposite sides ➡️ E isomers
  5. If double bond present then (eg between O and C) then O has to be counted twice
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8
Q

Why can’t but-1-ene or hex-1-ene etc have E-Z isomers

A

Same 2 groups attached to the C=C bond

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9
Q

What are the physical properties of alkenes

A
  • slightly polar - C=C bond
  • weak vdw
  • water insoluble
  • soluble in non-polar solvents
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10
Q

What is the definition of an unsaturated hydrocarbon

A

Contains at least one C=C or C(triplebond)C bond and is made of Carbon and Hydrogen only

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11
Q

What kind of reactions do Alkenes undertake

A

Addition reactions

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12
Q

What is the definition of bond length

A

The distance between the nuclei of two covalently bonded atoms

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13
Q

What is the definition of a sigma bond

A

A covalent bond formed by the linear overlap of atomic orbitals

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14
Q

Draw diagram of a sigma bond and draw its shape

A

See page 36 notes

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15
Q

What is the definition of a pi bond

A

A covalent bond formed by the sideways overlap of p orbitals

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16
Q

Draw diagram of a pi bond and draw its shape

A

See page 36

17
Q

What is the definition of an electrophile

A

An ion or molecule that attacks a region of high electron density

18
Q

Describe the addition of Cl2 to alkenes

A

Fast at room temp
If Alkene gas then passed through Cl2 solution
If Allene liquid then shaken with Cl2 solution

19
Q

Write the equation and mechanism for the addition of Cl2 to Alkene

A

See page 37 and 38

20
Q

How cal you detect if Br2 has been added to an alkene

A

Orange Br2 disappears

21
Q

Describe the process of the addition of HCl to alkene

A

Adds to ethene at 200°C

22
Q

At what temp does HBr add to an alkene

A

100°C

23
Q

What is the definition of heterolytic fission

A

Bond breaking in which both of the shared electrons go to one atom

24
Q

Draw and name the mechanism for the addition of HBr to ethene

A

See page 40

25
Q

What is the definition of primary carbocation

A

A carbocation which has one carbon atom directly bonded to the positively charged carbon

26
Q

What is the definition of a secondary carbocation

A

A carbocation which has two carbon atoms directly bonded to the positively charged carbon

27
Q

What is the definition of a tertiary carbocation

A

A carbocation which has three carbon atoms directly bonded to the positively charged carbon

28
Q

Draw the molecule usually formed when HBr is added to propene. Why is this formed and not the other

A

See page 41
Due to markovnikov’s rule- H will add to the carbon with the most H atoms already on it
Alkyl groups make carbocation more stable - push e towards positive C in carbocation

29
Q

What is the definition of Hydrogenation

A

Addition of a H molecule across a C=C

30
Q

Describe the process of catalytic hydrogenation

A

Alkene mixed with H2

Passed over finely divided Ni catalyst at 150°C

31
Q

What is the definition of catalyst

A

A substance which increases the rate of a chemical reaction but does not get used up

32
Q

What is the shape of alkenes

A

Bond angle of approximately 120°

Single plane

33
Q

What is the definition of polymerisation

A

Joining together of many small molecules (monomers) to form a large molecule

34
Q

What is the definition of a monomer

A

Many small molecules join together to form a polymer

35
Q

Describe the process of drawing a polymer

A
  1. Change double bond to single
  2. Draw bond angles at 90°
  3. Draw longer bond to right and left and draw bracket through these
  4. Add remaining atom symbols

AS Chemistry unit 2 (10 decks)

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