Alkenes

Question 1

What are alkenes

Answer 1

unsaturated hydrocarbons

Question 2

What types of bonds are involved in an alkene double bond

Answer 2

1 pi bond and 1 sigma bond

Question 3

What is a sigma bond

Answer 3

formed between 2 atoms where 2 orbitals overlap each other

Question 4

what is a pi bond

Answer 4

formed by the overlap of 2 p-orbitals

Question 5

where is the pi bond electron density situated

Answer 5

above and below the line where the sigma bond is formed

Question 6

why are alkenes unable to rotate around the double bond

Answer 6

pi bonds lock the carbon atoms in place

Question 7

What angle is formed by a carbon with double bond

Answer 7

120 degrees

Question 8

what causes a 120 degree angle to form between angles in an alkene around a carbon with a double bond

Answer 8

There are free bonds around the carbon meaning there are 3 regions of repulsion causing a 120 degree angle

Question 9

What is stereoisomerism

Answer 9

same structural formula, different arrangement of atoms in space

Question 10

What is E/Z isomerism

Answer 10

When rotation of atoms is restricted due to pi bonds leading to a fixed position

Question 11

Where does EZ isomerism occur

Answer 11

in double bonded compounds where carbons are attached either side of the bond

Question 12

Cis-Trans isomerism is what

Answer 12

when the carbon atoms are attached to methyl groups that are either opposite or the same side

Question 13

What is more reactive, alkanes or alkanes

Answer 13

alkenes

Question 14

what makes alkenes reactive

Answer 14

pi bonds, electrons are exposed to atoms causing it to break the double bond

Question 15

What makes pi bonds weaker than sigma bonds

Answer 15

bond enthalpy

Question 16

What type of reactions do alkenes undergo

Answer 16

addition reactions

Question 17

what happens in an addition reaction

Answer 17

a molecule will break the double bond of another molecule to allow the 2 reactants to form 1 product

Question 18

How does the hydrogenation of an alkene work

Answer 18

hydrogen gas reacts with the double bond of an alkene with the help of a nickel catalyst to form an alkane

Question 19

How does the halogenation of an alkene work

Answer 19

the hydrogen halide reacts with an alkene to break the alkene into an alkane with a carbocation where the hydrogen will react to help form a haloalkane

Question 20

What test can be used to test for unsaturated molecules

Answer 20

bromine water can be added

Question 21

what colour change is seen between bromine water if a C=C bond is present

Answer 21

orange —> colourless

Question 22

What is an electrophile

Answer 22

an electron pair acceptor

Question 23

What mechanism is seen in the reaction of an alkene to an alkane

Answer 23

electrophilic addition

Question 24

What mechanism is seen in the reaction of an alkene to an haloalkane

Answer 24

electrophilic addition

Question 25

What does a double bond represent

Answer 25

A region of high electron density due to pi bonds

Question 26

Describe the electrophilic addition of ethene with hydrogen gas

Answer 26

- ethene double bond exposed to hydrogen gas forming a carbocation of ethane and hydrogen -1 ion - The hydrogen -1 ion will react with the carbocation double bond which will form ethane

Question 27

What partial charges are formed in H-Br

Answer 27

H has delta + charge Br has delta - charge

Question 28

How are partial charges formed in a Br-Br molecule

Answer 28

The Br-Br molecule will come close to the double bond which causes the electrons in the Br-Br molecule to repel leading to induced dipoles forming where the has a positive and negative partial charge on each atom

Question 29

What type of bond fission occurs when a molecule reacts with a C=C bond

Answer 29

heterolytic fission

Question 30

What is a primary carbocation

Answer 30

when the carbocation is attached to 1 carbon

Question 31

what is a secondary carbocation

Answer 31

when a carbocation is attached to 2 carbons

Question 32

what is a tertiary carbocation

Answer 32

when a carbocation is attached to 3 carbons

Question 33

How can alkyl group be represented

Answer 33

-R

Question 34

What type of carbocation is the most stable

Answer 34

tertiary

Question 35

What type of carbocation is the least stable

Answer 35

primary

Question 36

what makes tertiary carbocations more stable than any other carbocation

Answer 36

the 3 carbon atoms push electrons into the carbon making it more positively charged leading to a more stable carbocation