chapter 13 - alkenes

Question 1

alkenes

Answer 1

a homologous series of unsaturated hydrocarbons that share the general formula CnH2n

Question 2

bonding in alkenes

Answer 2

contains double bonds (π bonds) as well as σ bonds

Question 3

σ bonds

Answer 3

orbitals directly between bonding atoms overlap

Question 4

π bonds

Answer 4

sideways overlap of adjacent p-orbitals above and below the bonding carbon atoms

Question 5

alkene shape

Answer 5

bond angles around C=C bond are 120° giving the molecule a trigonal planar shape around the C=C the π-bonds restrict rotation of the σ-bonds

Question 6

alkene properties

Answer 6

• alkenes are insoluble in water - alkene boiling points increase with chain length - alkenes have a lower boiling point than the equivalent alkane

Question 7

stereoisomerism

Answer 7

occurs in compounds with the same structural formula but a different arrangement of atoms in space

Question 8

when and why does E/Z isomerism occur?

Answer 8

caused by the π-bond restricting the rotation of the molecule can only occur if: - there is a C=C bond - each carbon is bonded to two different atoms

Question 9

E (entgegen) isomerism

Answer 9

atoms on opposite sides

Question 10

Z (zusammen) isomerism

Answer 10

atoms on the same side

Question 11

conditions of hydrogenation

Answer 11

150oC and nickel catalyst

Question 12

product of hydrogenation

Answer 12

alkane

Question 13

conditions of bromination

Answer 13

mix at RTP

Question 14

products of bromination

Answer 14

dibromoalkane

Question 15

conditions of reaction with hydrogen halides

Answer 15

mix at RTP

Question 16

products of reaction with hydrogen halides

Answer 16

halooalkane

Question 17

conditions of hydration

Answer 17

300oC, 60-70atm and H3PO4 catalyst

Question 18

products of hydration

Answer 18

alcohol

Question 19

electrophile

Answer 19

an electron pair acceptor

Question 20

step 1 of electrophilic addition

Answer 20

the π bond gives alkenes a region of high electron density which induces a dipole in non-polar molecules

Question 21

step 2 of electrophilic addition

Answer 21

the electron pair in the π bond is attracted to the atom with a positive dipole to form a covalent bond. the small molecule is broken by heterolytic fission which results in the formation of a positive carbocation and a negatively charged ion

Question 22

step 3 of electrophilic addition

Answer 22

a pair of electrons from the negative ion are donated to the positive carbon in the carbocation forming a covalent bond

Question 23

markownikov’s rule

Answer 23

states that (in the reaction of an alkene and hydrogen halide or water) the hydrogen being added bonds to the carbon with the most hydrogens present

Question 24

addition polymerisation

Answer 24

linking together of alkene monomers to form long chain saturated polymers