GUJCET 2016 Chemistry Question Paper with Answer and Solution

(D) Vitamin $B_1$ is chemically known as Thiamine.
It is a water-soluble vitamin that plays a crucial role in energy metabolism and nerve function.

(D) The reaction of $but-1-ene$ $(CH_3CH_2CH=CH_2)$ with various reagents is analyzed as follows:
$1$. $Br_2 / CCl_4$: Forms $1,2-dibromobutane$. The carbon at $C-2$ becomes chiral,resulting in a racemic mixture (optically inactive).
$2$. $HBr$: Forms $2-bromobutane$. The carbon at $C-2$ is chiral,resulting in a racemic mixture (optically inactive).
$3$. $H_2O / H^{+}$: Forms $butan-2-ol$. The carbon at $C-2$ is chiral,resulting in a racemic mixture (optically inactive).
$4$. $(BH_3)_2 / H_2O_2, OH^{-}$: Forms $butan-1-ol$. The product $CH_3CH_2CH_2CH_2OH$ does not contain any chiral carbon atom,making it inherently optically inactive.
While options $A$,$B$,and $C$ produce racemic mixtures (which are optically inactive),option $D$ produces a molecule that is achiral by structure. In standard competitive chemistry contexts,the formation of an achiral molecule is the definitive answer for 'optically inactive product'.

(C) The Reimer-Tiemann reaction of phenol with $CHCl_3$ and $NaOH$ yields salicylaldehyde ($2$-hydroxybenzaldehyde) as the final product.
The chemical formula of salicylaldehyde is $C_7H_6O_2$.
Structure: $A$ benzene ring with an $-OH$ group at position $1$ and a $-CHO$ group at position $2$.
Counting $\sigma$ bonds:
- $6$ $C-C$ bonds in the ring.
- $4$ $C-H$ bonds on the ring.
- $1$ $C-O$ bond (phenolic).
- $1$ $O-H$ bond.
- $1$ $C-C$ bond (between ring and $-CHO$).
- $1$ $C-H$ bond (in $-CHO$).
- $1$ $C-O$ bond (in $-CHO$).
Total $\sigma$ bonds = $6 + 4 + 1 + 1 + 1 + 1 + 1 = 15$.
Counting $\pi$ bonds:
- $3$ $\pi$ bonds in the benzene ring.
- $1$ $\pi$ bond in the $C=O$ group.
Total $\pi$ bonds = $3 + 1 = 4$.
Thus,the number of $\sigma$ and $\pi$ bonds are $15$ and $4$ respectively.

(A) Primary alcohols $(R-CH_2OH)$ are oxidized to aldehydes $(R-CHO)$ using mild oxidizing agents.
$PCC$ (Pyridinium chlorochromate) in $CH_2Cl_2$ is a selective oxidizing agent that stops the oxidation at the aldehyde stage.
Strong oxidizing agents like $KMnO_4$ (in acidic or basic medium) or $Na_2Cr_2O_7 + H_2SO_4$ (Jones reagent) oxidize primary alcohols directly to carboxylic acids $(R-COOH)$.

(D) The acidic strength of carboxylic acids depends on the stability of the carboxylate anion formed after the loss of a proton. Electron-withdrawing groups $(EWG)$ increase acidity,while electron-donating groups $(EDG)$ decrease it.
$A$. The inductive effect of the $-Cl$ atom decreases as its distance from the $-COOH$ group increases. Thus,the order is correct.
$B$. $-NO_2$ is an $EWG$ (increases acidity),and $-CH_3$ is an $EDG$ (decreases acidity) compared to benzoic acid. Thus,the order is correct.
$C$. The number of $-Cl$ atoms increases the electron-withdrawing effect,increasing acidity. Thus,the order is correct.
$D$. Formic acid $(HCOOH)$ is more acidic than acetic acid $(CH_3COOH)$ due to the $+I$ effect of the methyl group. However,benzoic acid $(C_6H_5COOH)$ is more acidic than acetic acid $(CH_3COOH)$ because the phenyl group is electron-withdrawing relative to the methyl group. Therefore,the correct order is $HCOOH > C_6H_5COOH > CH_3COOH$. The given order $HCOOH > CH_3COOH > C_6H_5COOH$ is incorrect.

(C) The chemical name of vitamin $B_1$ is Thiamine.
Vitamin $B_1$ is also known as aneurin.
Riboflavin is vitamin $B_2$,Pyridoxine is vitamin $B_6$,and $\alpha$-tocopherol is vitamin $E$.

(A) Many enzymes require metal ions as cofactors to function. Among the given options,$Mn^{2+}$,$Cu^{2+}$,and $Fe^{2+}$ are all known to act as essential cofactors for various enzymes. However,in the context of standard biochemical textbooks,$Mn^{2+}$ is frequently cited as a cofactor for enzymes like glycosyltransferases and decarboxylases. Since multiple options are technically correct in biological systems,the question is often context-dependent. Given the standard curriculum,$Mn^{2+}$ is the most common example provided for metal ion cofactors.

(A) The correct answer is $A$. $CCl_4$ is a toxic substance that can cause liver damage and skin irritation,but it does not specifically cause 'red rashes' as a primary chemical property in the context of standard chemistry textbooks. Option $B$ is correct as $CCl_4$ reacts with water vapor at high temperatures to produce phosgene $(COCl_2)$,a highly toxic gas. Option $C$ is correct as $CCl_4$ was historically used in fire extinguishers (Pyrene extinguishers). Option $D$ is correct as $CCl_4$ is a non-polar solvent,making it insoluble in water,and it possesses a characteristic sweet,aromatic odor.