3.3.3 - Haloalkanes

Question 1

How do you name haloalkanes?

Answer 1

Prefix: iodo-/chloro-/bromo-/fluoro-
(Can be preceded by di-/tri-/tetra-)
The halogens come in alphabetical order if there are multiple.

Question 2

What is the trend with boiling points of haloalkanes

a) with different chain lengths?
b) down group 7?
c) branching?

Answer 2

Trend with boiling points of haloalkanes,

a) longer chain lengths: higher bpt,
b) down group 7: higher bpt,
c) decreases with branching.

Question 3

How do the bpts of haloalkanes compare with those of similar chain length alkanes and why?

Answer 3

Higher. Due to higher Mr values and more polarity.

Question 4

Main intermolecular force between haloalkane molecules?

Answer 4

van der Waals’ intermolecular forces.

Question 5

Are haloalkanes soluble in water and why?

Answer 5

No: the carbon-halogen bond is not sufficiently polar.

Question 6

When are haloalkanes soluble? Use?

Answer 6

With hydrocarbons. Uses: dry-cleaning fluids to remove oily stains.

Question 7

What element is the most electronegative?

Answer 7

Fluorine.

Question 8

Bond polarity _______ down group 7.

Answer 8

Decreases.

Question 9

The bond becomes ____ polar down group 7.

Answer 9

The bond becomes LESS polar down group 7.

Question 10

What is the impact of electronegative halogen atoms covalently bonded to a carbon in haloalkanes?

Answer 10

Withdraws electron density from the carbon, leaving it susceptible to attack from nucleophiles.

Question 11

Bond enthalpy _______ down group 7. Why?

Answer 11

Bond enthalpy DECREASES down group 7. Because the atomic radii increase, so there is weaker attraction between the shared electrons in the covalent bond and the positive nuclei.

Question 12

Reactivity of haloalkanes ______ down group 7. Why?

Answer 12

Reactivity of haloalkanes INCREASES down group 7. Due to decreased bond enthalpies.

Question 13

Conditions and type of reaction?

a) Haloalkane -> alcohol
b) Haloalkane -> amine
c) Haloalkane -> nitrile

Answer 13

a) Primary alcohol
Aqueous solvent
Warm
Nucleophilic substitution
(KOH/NaOH dissolved in ethanol and water).

b) XS concentrated ethanolic ammonia and high pressure
c) aqueous ethanolic KCN

Question 14

How do you add a carbon atom to the carbon chain?

Answer 14

Nucleophilic substitution with aqueous ethanolic KCN to make a nitrile

Question 15

Define ‘nucleophile’.

Answer 15

Nucleophile: electron pair donor.

• A negative charged ion or has an electronegative ion.
• With a lone pair of electrons (on electronegative ion).

Question 16

Name of reaction: haloalkane -> alkene?

Answer 16

Elimination

Question 17

Conditions to form an alkene from a haloalkane?

Answer 17

Concentrated NaOH/KOH
Hot
Ethanolic solvent (ANHYDROUS)
Elimination
Tertiary alcohol

Question 18

Do secondary alcohols usually undergo nucleophilic substitution or elimination reactions with hydroxide ions?

Answer 18

Both! Depends on conditions.

Question 19

In elimination reactions, hydroxide ions act as ________.

Answer 19

Electrophiles.

Question 20

Uses of chlorofluorocarbons?

Answer 20

Short chain: aerosol propellants and refrigerants.

Long chain: dry cleaning and degreasing solvents.

Question 21

Equation of CCl3F to form a chlorine free radical?

Answer 21

CCl3F —UV—> CCl2F. + Cl.

Question 22

3x Equations showing reactions of chlorine free radicals with ozone? What is the catalyst?

Answer 22

1) .Cl + O3 -> ClO. + O2
2) ClO. + O3 -> Cl. + 2O2

Overall = 2O3 -> 3O2 with .Cl catalyst.

Question 23

Define ‘free radical’.

Answer 23

An uncharged molecule
typically highly reactive and short-lived
having an unpaired valency electron.