Halogen Derivatives

Question 1

How are halogen derivatives of hydrocarbons classified?

Answer 1

On the basis of hydrocarbon skeleton to which halogen is attached to giving haloalkanes , haloalkenes, haloarenes and on the basis of number of halogen atom on halogen derivatives giving di try and only halogen compounds

Question 2

On what basis are monohalogens classified?

Answer 2

On the basis of hybridization of carbon to which halogen is attached and position of halogen atom

Question 3

What are alkyl halides or haloalkanes

Answer 3

In which halogen atom is attached to so3 hybridized carbon which is a part of the saturated carbon skeleton. Are primary , secondary and tertiary ,

Question 4

What are allylic halides

Answer 4

Halogens are attached to sp3 hybridized Carbon atom which is attached to a carbon carbon double bond

Question 5

What are benzylic halide?

Answer 5

Halogen atom is bonded to sp3 carbon which is bonded to an aromatic ring

Question 6

What is vinyl is halide?

Answer 6

Halogen is bonded to sp2C of alicyclic chain

Question 7

What is haloalkyne?

Answer 7

Halogen is attached to sp hybridized carbon atom

Question 8

Aryl halides or haloarenes

Answer 8

Halogen atom is directly bonded to sp2 C of an aromatic ring

Question 9

How are alkyl halides named?

Answer 9

Named as haloalkanes… naming of alkyl group followed by name of halogen as halide

Question 10

How are alkyl halides prepared from alcohol?

Answer 10

By replacement of hydroxyl group by halogen atom using 3 ways - 1) halogen acids
2) phosphorus halide 3) thionyl chloride AND from hydrocarbons using addition of hydrogen halide to alkene i.e markonikov rule and peroxide effect

Question 11

Explain how halogen acid used to make haloalkanes

Answer 11

1) HCl+ Anhy. AlCl3 used for primary and secondary alcohols(LUCAS REAGENT)
2) Conc. HCl used for tertiary alcohols
3)NaBr+H2SO4 used to make HBr which reacts with R-OH to give R-Br
4)NaI + H3PO4 used to make HI which reacts with R-Oh to give R-I

Question 12

Explain how phosphorus halide used to make haloalkanes

Answer 12

1)PX3 (x= I Br Cl F) reacts with R-OH to make 3R-X + H3PO4
2) PCl5 (Phosphorus pentachloride) reacts with R-OH to give R-Cl+ HCl + POCl3

Question 13

Explain how thionyl chloride is used to make alkyl chloride

Answer 13

No extra efforts required in this reaction hence preferred
R-OH + SO2Cl2 makes R-Cl + SO2(gas) + HCl (gas)

Question 14

Explain how addition of hydrogen halide to Allene forms haloalkanes

Answer 14

By MKR rule (classical carbocation mechanism) , peroxide effect and reactivity if HX

Question 15

How are ALKYL IODIDES prepared easily?

Answer 15

Using alkyl chlorides and bromides with sodium iodide in methanol or acetone solution

Question 16

What is FINKELSTEIN REACTION?

Answer 16

RCl + NaI—————> RI + NaCl (ppt)
Acetone

Question 17

How are alkyl fluorides formed

Answer 17

Alkyl bromides and chlorides are heated with metal fluorides like AgF and SbF3

Question 18

What is SWARTZ REACTION

Answer 18

RCl + AgF——> RF + AgCl(ppt)

Question 19

What is SANDMEYERS REACTION?

Answer 19

Aryl halides can be prepared by replacement of diazonium salt.

Question 20

Why are alkyl halides moderately polar compounds?

Answer 20

Halogens are highly electronegative elements in comparison with carbon… hence polarity is developed on both atoms … carbon develops a partial positive charge and halogen develops a partial negative charge. Thus a carbon halogen bond in alkyl halide is a polar covalent bond.

Question 21

Why from iodine to fluorine bond enthalpy decreases

Answer 21

I to F size decreases
As C-X bond length increases , bond strength decreases because as the size of p-orbital of halogen increases the p-orbital becomes more diffused and extent of overlap with orbital of carbon decreases.

Question 22

What is the order increasing boiling point of alkyl halide?

Answer 22

RI> RBr> RCl >RF
Increasing atomic mass of halogen due to van der waals force

Question 23

What happens to boiling points of isomeric alkyl halides?

Answer 23

Boiling point decreases with increased branching as surface area decreases and van der waals forces decrease.

Question 24

Briefly explain solubility of alkyl halides

Answer 24

1) insoluble in water due to inability of forming hydrogen bonds with water as attraction between alkyl halides is stronger than that of alkyl halides and water
2)soluble in non polar organic solvents

Question 25

Briefly explain solubility of Aryl halides

Answer 25

1) insoluble in water
2)soluble in organic solvents
3) act as alkyl halides if not modified functional groups.
4) isomerism diahalobenzenes have same boiling points, but different melting points.
MP of para isomer is high due to symmetrical structure which leads to tightly packed lattice and stronger intermolecular forces…

Question 26

What are stereoisomers?

Answer 26

Isomers having the same bond connectivities or structural formulw

Question 27

What is a chiral carbon atom?

Answer 27

Carbon atom in a molecule which carries four different groups/atoms. Such a molecule cannot superimpose perfectly on its mirror image.
A chiral molecule and it’s mirror image are not identical.

Question 28

What is chirality?

Answer 28

The property of chiral molecules I.e the handedness (LHS and RHS) is called chirality

Question 29

What is optical isomerism?

Answer 29

The stereoisomerism in which the isomers have different spatial arrangements of groups/atoms around a chiral atom is called optical isomerism

Question 30

What plane polarized light?

Answer 30

ordinary light is passed through ✨Nicol’s prism✨—>Ppl released.

Light having oscillations only in one plane perpendicular to direction of propagation of light is known as ppl.

Question 31

What is optical activity?

Answer 31

The property of a substance by which it rotates plane of polarization of incident plane polarized light is called optical activity. Compounds which rotate the plane of plane polarized light are called optically active compounds and those which do not rotate the plane are called optically inactive compounds.

Question 32

What is optical rotation?

Answer 32

The angle through which a substance rotates the plane polarized light on passing it through.

Question 33

What are the directions of optical rotation?

Answer 33

Dextrorotatory and laveorotatory.
Dextrorotatory is when a compound which rotates the plane of plane polarized light towards right. Designated by (+) or d- sign

Laveorotatory is when a compound rotates the plane of plane polarized light towards left
Designated by (-) or l- sign.

Question 34

What are ENANTIOMERS?

Answer 34

The optical isomers which have equal and opposite optical rotation I.e. non superimposable mirror images of each other.
They have identical physical properties except sign of rotation
They have identical chemical properties except towards optically active reagent.

Question 35

What is a RACEMIC MIXTURE?

Answer 35

An equimolar mixture of enantiomers . RACEMIC modification is optically inactive because optical rotation due to molecules of new timers is cancelled by equal and opposite optical rotation due to molecules of other enantiomers.
Designated by +
-
Or (dl)

Question 36

What is a WEDGE FORMULA?

Answer 36

When a tetrahedral carbon is imagined to be present in the plane of paper all the four bonds at this carbon cannot lie in the same plane. The bonds projecting above the plane of paper are represented by a solid wedge and those below are represented by broken wedges (dashes)

Question 37

What is the laboratory test of haloalkanes?

Answer 37

On warming with aqueous sodium or potassium hydroxide , covalently bonded hydrogen in haloalkanes is converted to halide ion
R-X +OH- —> R-OH + X-
This reaction is acidified by adding dil. HNO3 and AgNO3 , this gives AgX (ppt) which confirms presences of halogen