haloalkanes

Question 1

explain the formation of alkyl halide and aryl halide

Answer 1

The replacement of hydrogen atom(s) in an aliphatic or aromatic hydrocarbon by halogen atom(s) results in the formation of alkyl halide and aryl halide

Question 2

what is the diff between Haloalkanes and haloarenes

Answer 2

Haloalkanes contain halogen atom(s) attached to the sp3 hybridized carbon
atom of an alkyl group whereas haloarenes contain halogen atom(s) attached to sp2
hybridized carbon atom(s) of an aryl group

Question 3

what is chloramphenicol used for?

Answer 3

Chlorine containing antibiotic produced by microorganisms is very effective for the
treatment of typhoid fever

Question 4

the deficiency of what can cause thyroxine

Answer 4

Our body produces iodine containing hormone, thyroxine, the deficiency of which causes a disease called goiter

Question 5

chloroquine is used for the treatment
of

Answer 5

malaria

Question 6

what is the classification of Haloalkanes and haloarenes Containing sp3 Carbon

Answer 6

Alkyl halides
Allylic halides
Benzylic halides

Question 7

explain alkyl halides

Answer 7

the halogen atom is bonded to an alkyl group (R). They form a homologous series represented by CnH2n+1X

Question 8

explain allylic halides

Answer 8

These are the compounds in which the halogen atom is bonded to an
sp3-hybridised carbon atom adjacent to carbon-carbon double bond
(C=C) i.e. to an allylic carbon

Question 9

explain Benzylic halides

Answer 9

These are the compounds in which the halogen atom is bonded to an
sp3-hybridised carbon atom attached to an aromatic ring.

Question 10

what is the classification of Haloalkanes and haloarenes Compounds Containing sp2 C

Answer 10

Vinylic halides
Aryl halides

Question 11

what is vinylic halides?

Answer 11

These are the compounds in which the halogen atom is bonded to a sp2-hybridised carbon atom of a carbon-carbon double bond

Question 12

what is Aryl halides?

Answer 12

These are the compounds in which the halogen atom is directly bonded to the sp2-hybridised carbon atom of an aromatic ring.

Question 13

what is geminal halides?

Answer 13

when both the halogen atoms are present on the same carbon atom of the chain

Question 14

what is vicinal halides

Answer 14

when halogen atoms are present
on adjacent carbon atoms

Question 15

Nature of C-X Bond (polarised or not polarised)

Answer 15

Halogen atoms are more electronegative than carbon, therefore, carbon-halogen bond of alkyl halide is polarised the carbon atom bears a partial positive charge whereas the halogen atom bears a partial
negative charge

Question 16

As we go down the group in the periodic table, the size of halogen
atom

Answer 16

increases

Question 17

_____atom is the smallest halogen and _______ atom is the largest

Answer 17

Fluorine and iodine

Question 18

Alkyl halides are best prepared from

Answer 18

alcohols

Question 19

Methods of Preparation of Haloalkanes from alcohols

Answer 19

The hydroxyl group of an alcohol is replaced by halogen on reaction with concentrated halogen acids like phosphorus halides or thionyl chloride

Question 20

why is thionyl chloride preferred more in Preparation of Haloalkanes from alcohols

Answer 20

Thionyl chloride is preferred because in this reaction alkyl halide is formed along with gases SO2 and HCl. The two gaseous products are escapable, hence, the reaction gives pure alkyl halides

Question 21

. The reactions of primary and
secondary alcohols with HCl require the presence of a catalyst, ______

Answer 21

ZnCl2

Question 22

Methods of Preparation of Haloalkanes with tertiary alcohols

Answer 22

the reaction is conducted by simply shaking the alcohol with concentrated HCl at room temperature Constant boiling
with HBr (48%) is used for preparing alkyl bromide

Question 23

Good yields of R—I may be obtained by

Answer 23

heating alcohols with sodium or potassium
iodide in 95% orthophosphoric acid

Question 24

The order of reactivity of alcohols
with a given haloacid is

Answer 24

3°>2°>1°

Question 25

The preparation of alkyl chloride is carried out by?

Answer 25

either by passing dry hydrogen chloride gas through a solution of alcohol or by heating
a mixture of alcohol and concentrated aqueous halogen acid.

Question 26

the methods of preparation of alcohol is not used to prep aryl halides because

Answer 26

because the carbon-oxygen bond in phenols has a partial double bond character and is difficult to break being stronger than a single bond

Question 27

Methods of Haloalkanes Preparation From Hydrocarbons

Answer 27

From alkanes by free radical halogenation
From alkenes ((i) Addition of hydrogen halides:, (ii) Addition of halogens)

Question 27

Preparation of haloalkanes from alkanes by free radical halogenation

Answer 27

Free radical chlorination or bromination of alkanes gives a complex mixture of isomeric mono- and polyhaloalkanes, which is difficult to separate as pure compounds. Consequently, the yield of any single
compound is low

Question 28

Preparation of haloalkanes from alkenes

Answer 28

(i) Addition of hydrogen halides; An alkene is converted to corresponding alkyl halide by reaction with hydrogen chloride, hydrogen bromide or hydrogen iodide Propene yields two products, however only one predominates as per Markovnikov’s rule
(ii) Addition of halogens ;addition of bromine inCCl4 to an alkene resulting in discharge of reddish brown colour
of bromine constitutes an important method for the detection of
double bond in a molecule The addition results in the synthesis of vic-dibromides, which are colourless

Question 29

Preparation of haloalkanes from Halogen Exchange

Answer 29

(i)Alkyl iodides are often prepared by the reaction of alkyl chlorides/bromides with NaI in dry acetone. This reaction is known as Finkelstein reaction
(ii)The synthesis of alkyl fluorides is best accomplished by heating an alkyl chloride/bromide in the presence of a metallic fluoride such as AgF, Hg2
F2 The reaction is termed as Swarts reaction

Question 30

Finkelstein reaction

Answer 30

R-X + NaI = R-I + NaX

Question 31

Swarts reaction

Answer 31

CH3-Br + AgF = CH3-F + AgBr

Question 32

method of Preparation of Haloarenes

Answer 32

(i) From hydrocarbons by electrophilic substitution
(ii) From amines by Sandmeyer’s reaction

Question 33

Preparation of Haloarenes From hydrocarbons by electrophilic substitution

Answer 33

Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts like iron or iron(III) chloride.

Question 34

problems caused during Preparation of Haloarenes From hydrocarbons by electrophilic substitution

Answer 34

The ortho and para isomers can be easily separated due to large difference in their melting points.
Reactions with iodine are reversible in nature and require the presence of an oxidising agent (HNO3,HIO4) to oxidise the HI formed during iodination. Fluoro compounds are not prepared by this method due to high reactivity of fluorine

Question 35

Preparation of Haloarenes From amines by Sandmeyer’s reaction

Answer 35

When a primary aromatic amine, dissolved or suspended in cold aqueous mineral acid, is treated with sodium nitrite, a diazonium
salt is formed. Mixing the solution of freshly prepared diazonium salt with cuprous chloride or cuprous bromide results in the
replacement of the diazonium group by –Cl or –Br

Question 36

Alkyl halides are _______ when pure

Answer 36

colourless However, bromides and iodides
develop colour when exposed to light.

Question 37

why the boiling points of chlorides, bromides and iodides are considerably higher than those of the hydrocarbons of comparable molecular mass

Answer 37

Due to greater polarity as well as higher molecular mass as compared to the parent hydrocarbon, the intermolecular forces of attraction (dipole-dipole and van der Waals)
are stronger in the halogen derivatives

Question 38

The boiling points of isomeric haloalkanes decrease with ______
in branching

Answer 38

increase

Question 39

why the para-isomers are high melting as compared to their ortho and meta-isomers

Answer 39

It is due to symmetry of para-isomers that fits in crystal lattice better as compared to ortho- and meta-isomers

Question 40

the solubility of haloalkanes in water is low why

Answer 40

In order to dissolve haloalkane in water, energy is required to overcome the attractions between the haloalkane molecules and break the hydrogen bonds between water molecules. Less energy is released when new attractions are set up between the haloalkane and the water molecules as these are not as strong as the
original hydrogen bonds in water

Question 41

haloalkanes tend to dissolve in organic solvents why

Answer 41

the new intermolecular attractions between haloalkanes and solvent molecules have much the same strength as the ones being broken in the separate haloalkane and solvent molecules.

Question 42

what are nucleophiles?

Answer 42

nucleophiles are electron rich species.
Therefore, they attack at that part of the substrate molecule which
is electron deficient

Question 43

what is nucleophilic substitution reaction

Answer 43

The reaction in which a nucleophile replaces already existing nucleophile in a molecule is called nucleophilic substitution reaction

Question 44

what are ambident nucleophiles

Answer 44

Groups like cyanides and nitrites possess two nucleophilic centres and are called ambident nucleophiles.

Question 45

how does nucleophilic substitution reaction take place

Answer 45

These two processes take place simultaneously in a single step and no intermediate is formed. As the reaction progresses and the bond between the incoming nucleophile and the carbon
atom starts forming, the bond between carbon atom and leaving
group weakens As this happens, the three carbon-hydrogen bonds of the substrate start moving away from the attacking nucleophile. In transition state all the three C-H bonds are in the same plane and the
attacking and leaving nucleophiles are partially attached to the carbon. As the attacking nucleophile approaches closer to the carbon, C-H bonds still keep on moving in the same direction till the attacking
nucleophile attaches to carbon and leaving group leaves the carbon. As a result configuration is inverted, This
process is called as inversion of configuration.