Organic Chemistry: Alkenes

Question 1

what is a sigma bond?

Answer 1

overlap of orbitals directly between the bonding atoms

Question 2

what is a pi bond?

Answer 2

formed by the sideways overlap of adjacent p orbitals above and below the bonding C atoms

Question 3

what are stereoisomers?

Answer 3

compounds with the same structural formula but with different arrangements of the atoms in 3 dimensional space

Question 4

what are cahn-ingold-prelog rules?

Answer 4

• the prefix e- or z- is based of the atomic numbers of the atoms
• e-: the atoms with the highest atomic number are on opposite sides
• z-: the atoms with the highest atomic number are on the same side of the double bond

Question 5

What is e/z isomerism?

Answer 5

e-: the atom with highest atomic number are on opposite sides
z-: the atom with the highest atomic number are on the same side

Question 6

What is cis/trans isomerism?

Answer 6

• cis: the same group attached is on the same side of the bond
• trans: the same group attached is on opposite sides of

Question 7

what are the 3 types of reaction for alkenes?

Answer 7

• combustion
• electrophilic addition
• addition polymerisation

Question 8

why is the combustion of alkenes unusual?

Answer 8

lots of other uses due to their reactivity

Question 9

what is the reaction to go from an unsaturated alkene to saturated alkane?

Answer 9

• addition of hydrogen
• NIckel catalyst
• 150 degrees celsuis

Question 10

what is addition of halogens to alkenes called?

Answer 10

halogenation - makes a di-substitued haloalkane

Question 11

how do you test for alkenes?

Answer 11

bromine water added to alkene - Br2(aq) - orange to colourless

Question 12

what does the addition of hydrogen halides to alkenes form?

Answer 12

haloalkane

Question 13

why is the addition of hydrogen halide to alkenes a possible problem?

Answer 13

• alkenes are unsymmetrical
• so a mixture of products are usually formed

Question 14

what is the reaction of an alkene with steam?

Answer 14

alkene + steam –> alcohol

Question 15

what is the formula for steam?

Answer 15

H2O(g)

Question 16

what acid catalyst is used when alkenes react with steam?

Answer 16

H3PO4 - phosphoric acid

Question 17

what is a polymer?

Answer 17

long molecular chain built up from monomers

Question 18

what is a monomer?

Answer 18

small molecule that combines with many other monomers to form a polymer

Question 19

what is addition polymerisation?

Answer 19

formation of a very long molecular chain by repeated addition reaction of many unsaturated alkene molecules

Question 20

what are biodegradable polymers?

Answer 20

• made from natural materials
• reduce reliance on crude oil
• naturally decompose

Question 21

what are photodegradable polymers?

Answer 21

• designed to contain bonds that are weakened by absorbing light - produces reactive radicals

Question 22

what type of rotation do pi bonds have?

Answer 22

restricted rotation

Question 23

what shape are alkenes?

Answer 23

• trigonal planar, 120 around each carbon in C=C of alkenes

Question 24

what are alkenes?

Answer 24

• unsaturated hydrocarbons containing a C=C bond comprising a pi bond and a sigma bond

Question 25

what impacts the reactivity of alkenes?

Answer 25

relatively low bond enthalpy of the pi bonds