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Flashcards in Alkenes Deck (16)
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1

Alkene structure

Unsaturated hydrocarbons
Cn H2n, branched alkenes
No general formula for cyclic and many double bonds

2

Double bond nature

Carbon atoms in a double bond have 3 sigma bonds and 1 pi bond
Pi bond, formed by 2 lengthway overlap of p orbitals
Locks 2 carbons, no rotation

3

Shape

Trigonal planar
3 electron dense areas in same plane

4

Stereoisomers

Same structural formula, different arrangement of atoms in space
E/Z isomerism, C=C
Optical isomers, wide range of compounds

5

E/Z isomers

Rotation about double bond is restricted, carbon fixed relative to each other due to rigid pi bond

C=C
Different groups attached to each carbon of double bond

Same side, Z
Different side, E

6

Cis-trans isomerism

Special case of E/Z isomerism
Attached groups to each carbon must be hydrogen

7

Cahn-Ingold-Prelog rules

Priority based on atomic no
Group with higher atomic no at first point of difference=higher

8

Reactivity of alkenes

More reactive than alkanes due to pi bond
Pi electrons exposed than sigma electrons, breaks more readily, addition reactions
Pi bond enthrall is weaker than sigma bond

9

Addition reactions of alkenes

Hydrogen with nickel catalyst
Halogens
Hydrogen halides
Steam in presence of an acid catalyst

10

Hydrogenation of alkenes, elec addition

Passed over nickel catalyst, form alkane

11

Halogenation of alkenes

Test for saturation
Bromine added across double bond, orange to colourless
Haloalkanes

12

Alkenes and hydrogen halides

Alkenes and gaseous hydrogen halides at room temp
If alkene a gas, reaction takes place when gases are mixed
Form haloalkane

13

Hydration reactions

Alkenes and steam in the presence of H3PO3 acid catalyst
Alcohol

14

Electrophilic addition reactions

Pi electrons attract electrophiles
Arrow must start at bond/lone pair
Arrow head to atom

15

Electrophile

Molecule that is attracted to electron rich centres, accepts electron pair

16

Markownikoff’s rule and action stability

Increase in structure
More stable
More likely to be produced
Positive charge decreases