Chapter 13 - Alkenes

Question 1

what are alkenes?

Answer 1

unsaturated hydrocarbons

Question 2

what is the general formula for alkanes?

Answer 2

CnH2n

Question 3

What type of bonds are formed in alkenes?

Answer 3

ó bond and pi bond

Question 4

how is a pi bond formed?

Answer 4

by the sideways overlap of two orbitals

Question 5

can the double bond rotate?

Answer 5

no

Question 6

what is the shape around each carbon atom in an alkene?

Answer 6

trigonal planar

Question 7

what is the bond angle around a carbon in an alkene?

Answer 7

120

Question 8

what is stereoisomerism?

Answer 8

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

Question 9

what are the requirements for E/Z isomerism?

Answer 9

• C to C double bond
• different groups attached to each carbon atom of the double bond

Question 10

what is the requirement for cis-trans isomerism?

Answer 10

one of the attached groups on each carbon of the double bond must be hydrogen

Question 11

which isomer has the hydrogens on the same side?

Answer 11

cis

Question 12

is a cis isomer a z or e isomer?

Answer 12

z

Question 13

is a trans isomer a z or e isomer?

Answer 13

e

Question 14

what is the Cahn - Ingold - Prelog nomenclature rule?

Answer 14

the atoms attached to each double bonded carbon are given a higher priority if they have higher atomic numbers

Question 15

if the groups of higher priority are on the same side, what isomer is it?

Answer 15

Z

Question 16

if the groups of higher priority are on the diagonal side, what isomer is it?

Answer 16

E

Question 17

why are alkenes more reactive than alkanes?

Answer 17

the pi electrons are more exposed than the electrons in the ó bond

Question 18

what are the four addition reactions of alkenes?

Answer 18

hydrogenation
halogenation
with hydrogen halides
hydration

Question 19

what is the hydrogenation of alkenes?

Answer 19

when an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K, an alkane is formed

Question 20

what is the halogenation of alkenes?

Answer 20

alkenes react with chlorine or bromine at room temperature

Question 21

what happens in the reaction with alkenes and hydrogen halides?

Answer 21

alkenes react with gaseous hydrogen halides at room temperature to form haloalkanes

Question 22

what is the hydration of alkenes?

Answer 22

when alkenes react with steam in the presence of a phosphoric acid catalyst to form an alcohol

Question 23

what is electrophilic addition?

Answer 23

the mechanism of alkenes in addition reactions to form saturated compounds

Question 24

what is an electrophile?

Answer 24

an atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair

Question 25

what are photodegradable polymers?

Answer 25

they contain bonds that are weakens by absorbing light to start the degradation