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FOR JEE

1. A good Williamson synthesis of ethyl methyl ether would be

What is wrong with the following proposed synthesis of ethyl methyl ether? First, ethanol is treated with acid to protonate the hydroxyl group (making it a good leaving group), and then methoxide is added to displace water.

Proton transfer ( acid- base) reactions are much faster than almost any other reaction. Methoxide will act as a base and remove a proton from the oxygen much faster than methoxide will act as a nucleophile and displace water.

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3. Can HF be used to cleave ethers? Explain.

How could you synthesize isopropyl propyl ether, using isopropyl alcohol as the only carbon-containing reagent?

4. Account for the following observations:

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Which on is resonating form?

Which form has major contribution?

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Rank the following compounds in order of decreasing acidity:

Resonance vs chemical equilibrium : A molecule, best described as a resonance hybrid, does not spent part of its time as one structure and part as another. If this occurs, it is called a chemical equilibrium. So resonance forms differ only in the distribution of electrons and never in the position of atoms. If we move an atom, we have written a chemical equilibrium. For example, the allyl cation does not spent part of its time as one of these structures and part of its time as the other. But these two forms are different electronic representations of the allyl cation. Hence this is resonance, not a chemical equilibrium.

The following figure does not represents resonance forms of the same allyl cation but a chemical equilibrium because two forms can exist in equilibrium as equilibrating species because it spent part of its time as allyl cation and part of its time as cyclopropyl cation.

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Isovalent and heterovalent resonance: When the different resonating structures of an ion or molecule contain the same number of covalent bonds, the resonance phenomena is called isovalent resonance, and when thedifferent resonating structures of an ion or molecule contain different number of covalent bonds, the resonance phenomena is called heterovalent resonance.

Cross Conjugation In a cross-conjugated compound, three groups are present, two of which are not conjugated with each other, although each is conjugated with the third. Some examples are benzophenone, triene and divinyl ether.

Isocyanic acid, HNCO. Indicate the most and least stable structures and give reasons for your choices. Give the structure of the hybrid.

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Why the coupling reaction with benzene diazonium chloride occurs in case of N,N-dimethyl aniline. But N,N,2,6-tetramethylaniline do not couple with the same reagent.

Rank these compounds by acidity in water:

Determine the partial negative charge on the oxygen atom in a bond. The bond length is 1.22Å*and the bond dipole moment is 2.30 D.

If there were a full negative charge on the oxygen atom, the dipole moment would be

Knowing that the dipole moment is 2.30 D, we calculate that the partial negative charge on the oxygen atom is about 0.4

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Formal charge

Formal charge is the charge assigned to individual atoms in a Lewis structure of a molecule or polyatomic ion.

The formal charge is given by:Formal charge = Number of valence electrons in neutral unbounded atom – (numberof all unshared electrons + ½ the number of all shared electrons).The sum of the formal charges on each atom equals to the net charge on the molecule.For example, in methyl anion, carbon has four valence electrons, two nonbondingelectrons, and a share in three covalent bonds. Thus the formal charge will be:Formal charge = 4- (2+ ½ x 6) = 4-5 = -1. Therefore, the carbon must be negativelycharged.

Calculate the formal charge on each atom.

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Summary of intermolecular force

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This procedure can be extended to compounds that contain hetero atoms such as oxygen halogen and nitrogen e.t.c.

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Indicate the most acidic hydrogen in each of the following molecules. Explain your reasoning.

The most acidic hydrogen is marked in the bold

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o- Cyanoaniline is a much weaker base than aniline. Present a resonance argument to explain the effect of the substituent. A cyano substituent is strongly electron-withdrawing. When present at a position ortho to an amino group on an aromatic ring, a cyano substituent increases the delocalization of the amine lone-pair electrons by a direct resonance interaction.

The basicity constants of N, N- dimethylaniline and pyridine are almost the same, whereas 4-( N, N- dimethylamino) pyridine is considerably more basic than either. Identify the more basic of the two nitrogens of 4-( N, N- dimethylamino) pyridine, and suggest an explanation for its enhanced basicity as compared with pyridine and N, N- dimethylaniline

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There is no obvious reason why the dimethylamino group in 4-(N,N-dimethylamino)pyridine should be appreciably more basic than it is in N,N-dimethylaniline; it is the ring nitrogen of 4-(N,N-dimethylamino)pyridine that is more basic. Note that protonation of the ring nitrogen permits delocalization of the dimethylamino lone pair and dispersal of the positive charge.

Although fluorine is more electronegative than bromine p- fluorobenzoic acid is less acidic than p-bromobenzoic acid. - explain

Two probabilities are there, whether the base abstracts acetylinic H or hydroxyl H. because the hydroxyl H (pKa 17) is more acidic than acetylinic hydrogen (pKa 25) alkoxide ion will be formed.

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β-hydroxy acid on heating produces unsaturated acid.