DF.6

Question 1

What is meant when an organic compound is described as unsaturated?

Answer 1

It contains a double or triple bond between carbon atoms which means that it does not have as many hydrogen atoms as it could have with the number of carbon atoms in the compound?

Question 2

What type of hydrocarbon are alkenes? Saturated or unsaturated?

Answer 2

Unsaturated because they have a double bond.

Question 3

What is the general formula for non cyclic alkenes?

Answer 3

CnH2n, where n is the number of carbon atoms and can be any whole number.

Question 4

What suffix is used to indicate an alkene?

Answer 4

-ene

Question 5

How can the position of the double bond be indicated in the name?

Answer 5

Using a number, for example but- 2-ene, is CH3CH=CHCH3.

Question 6

What is a σ-bond?

Answer 6

When a pair of electrons are shared and arranged between the two atoms in the molecule orbital. The overlapping of the s orbitals give rise to the a σ-bond.

Question 7

As well as a σ-bond, what other type of bond is also there in a double bond?

Answer 7

𝛑-bond.

Question 8

What does a 𝛑-bond look like?

Answer 8

It consists of two areas of negative charge, one above and other below the line of the atoms.

Question 9

When looking bond enthalpies, why is the double bond never as strong as doubled the single bond?

Answer 9

Because the 𝛑-bond is not as strong as the σ-bond.

Question 10

What are electrophiles?

Answer 10

Substances that are capable of accepting a pair of electrons to form a covalent bond.

Question 11

Why are electrophiles attracted to the alkene’s double bond?

Answer 11

Because the double bond is a region of high negative charge density, and positive ions or molecules with a partial positive charge will be attracted towards this negative region, they act as electrophiles.

Question 12

What is a general test for unsaturation in an organic compound?

Answer 12

Bromine water. Alkenes will decolorize the orange brown bromine water.

Question 13

What is a reaction mechanism?

Answer 13

A visual way of showing the movement of electrons that is logically decided using ideas of bond polarity and charges.

Question 14

What happens to the bromine molecule as it approaches the alkene?

Answer 14

It becomes polarized, this means that the electrons in the bromine are repelled by the electrons in the alkene, and electrons are pushed back along the molecule, making the bromine atom nearer to the alkene slightly more positive and the other slightly more negative.

Question 15

What is the symbol used to represent the polarized bromine molecule?

Answer 15

Brδ+ - Brδ-

Question 16

What happens to the movement of the electrons when the bromine with δ+ acts as an electrophile and react with the alkene’s double bond?

Answer 16

A pair of electrons from one carbon goes onto forming a covalent bond with the bromine with δ+, and both the electrons that form the covalent bond between the bromine atoms go on to the bromine with δ-, making it Br- ion and the other carbon atom in the double bond a + ion with only six electrons.

Question 17

What is the carbon atom that has become positively charged in the intermediate step known as?

Answer 17

Carbocation.

Question 18

What then happens with the carbocation and the Br- ion?

Answer 18

Carbocation reacts rapidly with anything that has electrons to share. Therefore a pair of electrons from the Br- ion move onto the carbocation to form a new covalent bond of Br-C.

Question 19

What is an addition reaction?

Answer 19

A reaction where two or more molecules react to form a single larger molecule.

Question 20

What is it called when an addition reaction is initiated by an electrophile?

Answer 20

Electrophilic addition.

Question 21

What type of reaction is it when water is added to an alkene?

Answer 21

Hydration reaction.

Question 22

What is the product when alkene undergoes a hydration reaction?

Answer 22

An alcohol.

Question 23

What are the conditions for making industrial alcohol by hydrating an alkene?

Answer 23

High temperature and pressure in the presence of phosphoric acid catalyst.

Question 24

What other substance is used in a lab when hydrating an alkene?

Answer 24

Concentrated sulfuric acid.

Question 25

What are the conditions for hydrogenation of alkenes industrially?

Answer 25

150℃ with a pressure of 5 atmosphere, with powdered nickel catalyst.

Question 26

What are the conditions for hydrogenation of alkenes in a lab?

Answer 26

Standard laboratory conditions - room temperature and pressure, with platinum catalyst.