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Give reasons for the following : (i) Molecular mass of ethanol and dimethyl ether is the same, however ethanol is a liquid at room temperaturebut dimethyl ether is a gas. (ii) Anhydrous CaCl_(2) cannot be used for drying ethanol (iii)tertiary Alcohols form the turbidity fastest in Lucas test while primary alcohols form slowest. (iv) Ethyl alcohol reacts with HI but not with HCN. (v) Sodium metal can be used for drying diethyl ether but not ethanol. (vi) Propanol, unlike propane is soluble in water. (vii) Propanol boils at a higher temperature than propane. (viii) Why glycerol has high viscosity and is miscible with water in all proportions ? (ix) Reactivity of HX with alcohols is in the order, HI gt HBr gt CHl gt HF (x) Why is it not posssible to obtain a halide by reacting ROH with X^(-) ? (xi) ClCH_(2)CH_(2)OH is stronger acid than CH_(3)CH_(2)OH. (xii) Hydration of 3-phenylbut-1-ene in dil. H_(2)SO_(4) forms 2-phenylbutan-2-ol instead of 3-phenylbutan-2-ol. (xiii) The compound (CH(3))_(2)C-CH(OH)CH_(3) on treatment with conc. HCl forms (CH_(3))_(2)C(Cl)-CH(CH_(3))_(2) instead of (CH_(3))_(3)C-CH(Cl)CH_(3) (xiv) Acid catalysed dehydration of t-butanol is faster than that of n-butanol. (xv) When t-butanol and n-butanol are separately treated with a few drops of dilute KMnO_(4), in one case only, the purplecolour disappears and a brown precipitate is formed. Which of the two alcohols gives the above reaction and what is brown precipitate ? |
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Answer» (ii) tertiary Alcohols form an addition compound with `CaCl_(2)`. (iii) Positive inductive EFFECT is maximum in tertiary alcohol and hence-OH removal is facilitated. (iv) `C_(2)H_(5)OH` is a weak base and hence reacts with stronger acid. (v) Ethanol has active hydrogen atom which reactsw ith sodium. (vi) Propanol , unlike propane is soluble in water. (vii) In propanol,there is intermolecular hydrogen bonding but in propane, there is no hydrogen bonding . (viii) Hydrogen bonding is responding for high viscosity and solubility in water. (ix) Bond dissociationenergy of HX is in the order. (x) `OH^(-)` is a very poorleaving GROUP. Acid CONVERTS it to `H_(2)O`, a better leaving group. (xi) The electron withdrawing Cl delocalises the negative charge on the oxygen atom of the OH group. (xii) Hydration gives an intermediate `2^(@)C`, which undergoes a hydride shift to more stable `3^(@)` carbocation. `(##GRB_ORG_CHM_P2_C10_E01_015_A01##)` (xiii) The first formed `2^(@)C^(+)` rearranges by a `CH_(3)` shift to more stable `3^(@)C^(+)`, which tehn gives the `3^(@)` chloride. (xiv) The acid catalysed dehydration of an alcohol proceeds via the formation of a carbocation `:` `H-underset(H)underset(|)overset(H)overset(|)(C)-underset(OH)underset(|)overset(CH_(3))overset(|)(C)-CH_(3)overset(+H^(+))(hArr)H-underset(H)underset(|)overset(H)overset(|)(C)-underset(.^(+)OH)underset(|)overset(CH_(3))overset(|)(C)-CH_(3)underset((-H_(2)O))(hArr)H-underset(H)underset(|)overset(H)overset(|)(C)-underset(+)overset(CH_(3))overset(|)(C)-CH_(3)overset(-H^(+))(hArr)H-overset(H)overset(|)(C)=overset(CH_(3))overset(|)(C)-CH_(3)` (xv) n-Butanol is oxidised by `KMnO_(4)` and not t-butanol as the latter does not contain H atom ATTACHED to carbinol carbon atom. `underset((1^(@)"alcohol"))underset"n-Butanol"(CH_(3)CH_(2)CH_(2)CH_(2)OH)+underset(("Purple"))(KMnO_(4))rarr underset("Potassium benzoate")(CH_(3)CH_(2)CH_(2)COoverset(-)(O)overset(+)(K))+underset("Brown ppt.")(MnO_(2))+KOH` `underset((3^(@)"alcohol"))underset("tert-Butanol")(CH_(3)-underset(OH)underset(|)overset(CH_(3))overset(|)(C)-CH_(3))+KMnO_(4)rarr ` No reaction |
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