Alkenes

Question 1

Double bond details

Answer 1

-in a carbon-carbon single bond an electron pair is shared. This is called a sigma bond. Rotation of ch3 groups does not affect the sigma bond. The structure interconvert at room temp because rotation around the single bond is not restricted.
-in a double bond two electron pairs are shared. One pair is a sigma bond, one pair is a pi bond.
-rotation of a ch2 would require the pi bond to be broken therefore rotation is restricted

Question 2

Cis trans stereoisomers

Answer 2

-cis isomers have the same atoms/groups on the same side of the double bond
-trans isomers have the same atoms/groups on opposite sides of the double bond

Question 3

Stereoisomers

Answer 3

Compounds with the same numbers and types of atoms and have the same atom-atom bonding sequence but they have a different arrangement of atoms in space.

Question 4

E-Z nomenclature

Answer 4

To assign the configuration about a double bond as either E- or Z- one must first assign relative priorities to the two substituents bonded to each of the double-bonded carbons.

Priorities depend on atomic number. Atoms of higher atomic number are assigned higher priorities.

If the atom directly bonded to the double-bonded carbons is the same for two or more of the substituents, compare the atomic number of the second atoms out, and then the third, and so on, until a difference becomes apparent.

Also a doubly-bonded carbon in a substituent group (one of a, b, c or d) is assigned a higher priority than a singly-bonded carbon.

Question 5

Comparing addition reactions

Answer 5

Addition to an alkane has two products e.g. CH3CH2CH2CH2CH3 +Br2 = CH3CHCHCH2CHCH3 +H2
| |
Br. Br

Addition to a Alkene has one product CH3CH=CHCH3 + Br2 = CH3CHCHCH3
| |
Br Br

Question 6

Markovnikoff’s rule

Answer 6

In addition of HX to an alkene, the H becomes bonded to the carbon already bearing the larger number of hydrogens.

Haloalkanes are classed as primary, secondary or tertiary depending on how many carbons are bonded to the carbon bearing the halogen.

The major product above is secondary because there are two carbons bonded to the carbon bearing chlorine.
The minor product is primary because there is one carbon bonded to the carbon bearing chlorine.
Tertiary haloalkanes have three carbons bonded to the carbon bearing the halogen.

In the major product of an addition reaction, halogen becomes bonded to the original doubly-bonded carbon which has the fewer hydrogens.

Therefore tertiary haloalkanes are formed in preference to secondary ones which are formed in preference to primary ones

Question 7

Addition polymers

Answer 7

-Carbon backbone contains only carbons around double bond.

Question 8

Nucleophiles and electrophiles

Answer 8

Electrophile= (electron lover)electron accepter
Nucleophiles= (nucleus lover) can donate electrons

Nucleophiles are electron rich due to the presence of a pi bond or an atom bearing a non-bonding electron pair

Electrophiles are positive atoms e.g. metal cations or hydrogen ions