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OCR H032 AS Chemistry > Alkenes > Flashcards

Flashcards in Alkenes Deck (26)
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1
Q

Define alkene

A

An unsaturated hydrocarbon with a least 1 carbon to carbon double bond

2
Q

What is the general formula of an aliphatic alkene

A

CnH2n

3
Q

Which alkanes don’t follow the general formula

A

Cyclic alkenes and alkenes with more than 1 double bond

4
Q

What are the two types of bonds called in the double bond

A

Sigma and pi

5
Q

Where’s the sigma bond in the double bond

Describe the electrons

A

X
C———C
X

Equal from each carbon atom one above and one the line

6
Q

Describe the p bond in the double bond

A

Made from two sideways overlapping p orbitals from each carbon atom each carbon atom contributes 1 electron one pi bond consists of 2 regions one above the molecule and one below. This is why the molecule is flat (planar ) around the bond

7
Q

Which bond stops rotation

A

The pi bond

8
Q

What shape is around the double bond

A

Trigonal planar

9
Q

Why is the region around the bond trigonal planar

A

There are three regions of electron density around each of the carbon atoms
The three regions repel each other as far as possible
All the atoms are in the same plane

10
Q

What is the bond angle around a double bond

A

120 degrees

11
Q

What are stereoisomers

A

They have the same structural formula but a different arrangement of atoms in space

12
Q

How does stereoisomerism arise

A

Rotation around the double bond is restricted and the groups attached to each carbon atom are therefore fixed relative to each other

13
Q

What are the conditions for E/Z isomerism

A

A c=c bond

Attached to different groups (has to be one of a group either side of the bond)

14
Q

Which one (E or Z) is for when the groups are on the same side of the double bond

A

Z (Zame side)

E Ecross

15
Q

Which group gets priority to decide if it’s a E or Z isomer

A

The highest atomic number on each side of the double bond

16
Q

Do E/Z isomers have the same or different chemical properties and why?

A

The same because they have the same functional group

17
Q

What’s the difference between e/z isomers and cis/trans isomers

A

Cis/trans has to have hydrogen

18
Q

What is needed for hydrogenation of alkenes

A

Nickel catalyst
150 degrees
H2 under pressure

19
Q

What are the conditions in halogenation

A

Rtp

20
Q

What are the conditions of halogenation with a hydrogen halide

A

Rtp

Concentrated Hx

21
Q

What is Markovnikoff’s rule

A

When a molecule of Hx reacts with a non symmetrical alkene the major product is the one in which the H-atom attaches itself to the carbon atom already carrying a larger number of hydrogens

22
Q

Which carbocation is the most stable and why
A) primary
B) secondary
C) tertiary

A

C) tertiary because each alkyl group donates and pushes electrons towards the positive charge of the carbocation. The positive charge is spread over the alkyl groups . The more alkyl groups attached to the positively charged carbon atom, the more the charge is spread out, making the ion more stable

23
Q

What is the mechanism called for alkenes

A

Electrophilic addition

24
Q

What is an electrophile

A

An electron pair acceptor

25
Q

Why does the double bond in alkenes have a high electron density

A

Because of the presence of pi electrons

26
Q

What is attracted to the high electron density

A

Electrophiles