Basic Concepts & Hydrocarbons

Question 1

What are structural isomers?

Answer 1

Compounds with the same molecular formula but different structural formulas
Eg. Different placement of functional group or alkyl chain, different functional groups(ketone/aldehyde)

Question 2

What are stereoisomers?

Answer 2

Organic compounds with the same with the same molecular formula and structural formula but a different arrangement of atoms in space
Eg. Double bond will not allow atoms to rotate freely

Question 3

What are the Cahn-Ingold-Prelog rules?

Answer 3

1. locate the c-c double bond in the molecule and redraw to show substituents.
2. Assign priority of each substituent based on it’s mr, substituent with the highest mr is given the highest priority.
3. if the highest priority groups are on the same side of the c-c double bond the isomer is Z if they are on different sides then the isomer is E.

Question 4

What is Cis-Trans isomerism?

Answer 4

A type of E/Z isomerism where two substituents on each carbon atom are the same.
E is a trans isomer and Z is a Cis isomer

Question 5

What is homolytic fission?

Answer 5

When a covalent bond breaks and each electron goes to a different bonded atom. This generates two reactive neutral species called radicals

Question 6

What are radicals?

Answer 6

Highly reactive, neutral species which have one or more unpaired electrons shown as dots

Question 7

What is heterolytic fission?

Answer 7

When a covalent bond breaks and both electrons go to one of the bonded atoms this results in one anion and one cation

Question 8

What is covalent bond formation?

Answer 8

When two radicals or oppositely charged ions collide

Question 9

What are carbocations?

Answer 9

Very reactive, unstable intermediates

Question 10

Explain bonding in alkanes

Answer 10

• Each covalent bond has direct overlap of the electron clouds from each atom making a sigma bond (C-H and C-C)
• every carbon atom has a tetrahedral shape; bond angle 109.5

Question 11

Are alkane molecules polar? Why?

Answer 11

• they are non-polar
• carbon and hydrogen have a similar electro negativity
• London forces/induced dipole dipole forces are the intermolecular forces due to instantaneous charge distribution

Question 12

How does chain length effect the boiling points of alkanes?

Answer 12

• Boiling point increases as molecules increase in size

- this is due to increased intermolecular forces due to larger surface contact between adjacent molecules of

Question 13

How does branching effect boiling point?

Answer 13

• branched molecules can’t fit together as nearly
• fewer surface area interactions
• weaker intermolecular forces due to fewer London forces

Question 14

What do alkanes have low reactivity?

Answer 14

• all the covalent bonds have high bond enthalpies

- C-H sigma bonds have low polarity

Question 15

What does complete combustion of alkanes look like?

Answer 15

A blue flame will be produced

Question 16

What will incomplete combustion of alkanes look like? And what is produced?

Answer 16

A dirty yellow flame is produced

Water, carbon dioxide and carbon monoxide (CO)

Question 17

What are the 3 states of radical substitution?

Answer 17

1. Initiation- formation of the radicals
2. propagation- two repeated steps that build up the desired product in a side-reaction.
3. termination-two radicals collide to make a stable product.

Question 18

Explain the bonding in alkenes

Answer 18

Double covalent bond has two sections:

• two sigma bonds are formed by electron clouds of two carbon atoms overlapping
• pi bonds are formed by the electrons in adjacent p-orbitals overlapping above and below the carbon atoms(can only take place after a sigma bond is formed)

Question 19

Which is weaker pi bond or sigma bond?

Answer 19

Pi bond is weaker

Question 20

What are electrophiles?

Answer 20

Species that are electron pair acceptors

Question 21

What is hydrogenation?

Answer 21

The addition of hydrogen across a c-c double bond

-hydrogen and alkene are mixed and passed over a nickel catalyst at a temp of 150 degrees c

Question 22

What is halogenation?

Answer 22

Addition reaction when a halogen is added across a c-c double bond
Alkene becomes saturated producing a dihaloalkane

Question 23

How can you test for an unsaturated compound?

Answer 23

When bromine solution or iodine solution is mixed with a saturated compound- no reaction
Unsaturated compound- decolorisation

Question 24

What is hydration?

Answer 24

Addition reaction between a gaseous alkene and steam - used to make alcohols
-requires 300 degrees c phosphoric acid catalyst

Question 25

How can you carry out the addition of hydrogen halides to an alkene?

Answer 25

Hydrogen halides are gases at room temperature, these reactants are bubbled through the alkene
-produces a haloalkane

Question 26

What carbon will the halide bond with when a hydrogen halide is added to an unsymmetrical alkene?

Answer 26

When H-X is added to an unsymmetrical alkene the hydrogen becomes attached to the carbon with the most hydrogen atoms attached to it

Question 27

How are polymers formed from alkenes?

Answer 27

The pi bond within the c-c double bond is broken and the electrons from the pi bond form sigma bonds with neighbouring molecules

Question 28

How can you draw the structure of polymers?

Answer 28

Draw square brackets and add a subscript ‘n’

Question 29

What is a homologous series?

Answer 29

Substances that share the same functional group with successive members differing by one CH2 unit

Question 30

What are aliphatic hydrocarbons?

Answer 30

In which the carbon atoms are joined together in branched or unbranched chains

Question 31

What are alicyclics hydrocarbons?

Answer 31

In which the carbon atoms are joined together in a ring structure but are not aromatic

Question 32

What are aromatic hydrocarbons?

Answer 32

Where there is at least one benzene ring in the structure