JEE Advanced (Single Correct MCQs): Organic Chemistry - Some Basic Principles & Technique - JEE MCQ

NOTE : The phenomenon of resonance gives identical bonding and hence identical bond lengths.

C – C bond order in benzene = 1.5

TIPS/Formulae :

The bond length decreases in the order.

On the basis of the size of the hybrid orbitals, sp orbital should form the shortest and sp³ orbital the longest bond with other atom.

The first three are isomers of diethyl ether, C₂H₅OC₂H₅ (C₄H₁₀O).

TIPS/FORMULAE :

–NO₂, –Cl and –OH are electron-attracting or withdrawing group due to –M, –E and/or –I effects where as –CH₃ show, +I effect (electron releasing).
Because of the + I effect of the CH₃ group, toluene has the highest electron density in the o- and p- positions and hence can be most readily sulphonated.

Hybridisation in 

TIPS/Formulae :
cis-trans – Isomerism is due to restricted rotation either due to carbon-carbon double bond or due to cyclic structure.
NOTE : Geometrical Isomerism : The isomers which possess the same structural formula but differ in the spatial arrangement of the groups around the double bond are known as geometrical isomers.

[Note : dipole moment is a vector quantity].

Car bon bonded with a triple bond (i.e. C₁) is sp hybridised. Carbon bonded with a double bond (C₂) is sp² hybridised.

TIPS/Formulae :
For knowing the possible isomers of the compound follow the following points.
(i) First write down the possible number of isomeric parent alkane.
(ii) Introduce the given functional group at different positions so as to get different isomeric compound.
There are 5 isomers possible for C₆H₁₄.

The bond angle in sp³, sp² and sp hybridization is respectively 109.28', 120º and 180º.
Tetrachloroethene being an alkene has sp² hybridised C-atoms and hence the Cl – C –  Cl angle is 120º, whereas in tetrachloromethane, carbon is sp³ hybridised, so the angle is 109º.28’.

C₂H₆ is a saturated hydrocarbon and its carbon is sp³ hybridised. Hence it is least electronegative among alkanes, alkenes and akynes with the result C – H bond length will be maximum.

CH₂ = CH – C ≡ CH;
No of s bonds = 2 + 1 + 1 + 1 + 1 +1 = 7;
No of  π bonds = 1 + 2 = 3

NOTE : Heterolytic fission occurs when the two atoms differ considerably in their electronegativities.
O – H bond undergoes cleavage most readily because O and H differ markedly in their electronegativity and further oxygen being highly electronegative can accommodate the negative charge more effectively developed after the cleavage.

NOTE : The order of stability of carbonium ion is

tertiary > secondary > primary > methyl

Tertiary carbonium ions (formed in b) are more stable because of electron repelling (+I effect) nature of CH₃ group due to which the +ve charge gets dispersed and also due to hyperconjugation.

At 298 K, CO₂ and SO₂ exist as gases while H₂O exists as liquid.

Stereoisomers which are mirror image of each other are enantiomers and the one which are not mirror images are diasteromers. Conformation of the molecule is the spatial arrangement of the atoms of a given molecular structure that are obtained merely by rotation about a sigma bond in the molecule.

A compound which consists of at least one asymmetric carbon atom is capable of showing the phenomenon of optical isomerism.
The structure cannot show geometrical isomerism as one of the carbons along the double bond has identical group (methyl). Tautomerism is not possible because of the absence of –CO, group. It shows optical isomerism because it has chiral C atom with four different groups, H, CH₃, COOH and (CH₃),C = CH.

The above structure of allyl isocyanide clearly shows 5 C – H (σ), 2 C – C (σ), 1C – N (σ), 1N – C(σ), 1C – C (π), 2N– C (π) bonds, i.e., 9σ and 3π bonds in all. There are 2 non-bonded electrons on the C-atom (co-ordinate bond between N and C, the electron pair of N is shifted towards C).

TIPS/Formulae :

The stability of carbonium ion is influenced by both resonance and inductive effect.

NOTE : –NO₂ is an electron-attracting group where as –CH₃ is an electron-releasing group.

An electron - attracting substituent tends to dispersethe negative charge of the phenoxide ion and thus, makes it more stable. This, in turn, increases the acid strength of phenol. The substituent in para position is more effective than in the meta position as the former involves a resonating structure bearing negative charge on the carbon attached to the electron - withdrawing substituent.

An electron - releasing substituent tends to intensify the negative charge of the phenoxide ion and thus makes it more unstable. This, in turn, decreases the acid strength of phenol. Hence, the order of acid strength is

Dipole moment of p-dichlorobenzene is zero because of symmetrical structure. o- and m-dichlorobenzene have higher dipole moments than toluene due to high electronegativity of chlorine than –CH₃ group. Further, the o-dichlorobenzene has higher dipole moment due to lower bond angle than the m-isomer. Hence, the order of increasing dipole moment is :
p-dichlorobenzene (IV)  <  toluene (I) < m-dichlorobenzene (II)  <  o-dichlorobenzene (III)

The stereoisomers of butane -2,3-diol are

TIPS/Formulae :

Glyceraldehyde is taken as arbitrary standard for D, L – nomenclature.