Chemistry Case study (4 Marks)

1. (d) Anomers.

Explanation:

$\alpha$-D-( + )-glucose and $\beta$-D-( + )-glucose differ in configuration at C₁ (i.e., anomeric or glycosidic carbon) and hence are called anomers.

2. (b) An aldohexose.

Explanation:

This structure is an example of pyranose and aldohexose. Here, the carbohydrate's structure is of the $\beta$-pyranose fonn.

3. (a) C-1

Explanation:

C-1 is the anomeric carbon.

4. (d) Isomers of glucose that differ in configuration at carbon one (C-1).

Explanation:

Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration at C-1, if they are aldoses or in the configuration at C-2 if they are ketoses.

5. (d) 64%

Explanation:

Ordinary glucose is CL-glucose, with a fresh aqueous solution having specific rotation, $[\alpha]_\text{D}=+111^\circ.$ On keeping the solution for sometime, $\alpha$-glucose slowly changes into an equilibrium mixture of $\alpha$-glucose (36%) and $\beta$-glucose(64%) and the mixture has specific rotation + 52.5°

1.  (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

2. (d) Assertion is wrong statement but reason is correct statement.

Explanation:

All amino acids except glycine are optically active because they contain, asymmetric carbon atom. They exist in both D and L-forms. Most naturally occurring amino acids have L-configuration.

3. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

Explanation:

In $\alpha$-helix structure, the formation of hydrogen bonds takes place between -CO- and -NH groups, whereas in $\beta$-pleated structure, hydrogen bonds are formed between amide groups of two different chains.

4. (c) Assertion is correct statement but reason is wrong statement.

Explanation:

Out of 20 amino acids, only 10 amino acids can be synthesised by human body.

5.  (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. 

1.  (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

2. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

Explanation:

$\ \text{CHO}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COOH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COOH}\\\ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\$\text{CHOH})_4\xrightarrow[\text{HNO}_3]{[\text{O}]}(\text{COOH})_4\xleftarrow[\text{[O]}]{\text{HNO}_3}(\text{CHOH})_4\\\ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \text{CH}_2\text{OH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COOH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_2\text{OH}\\\ \text{Glucose}\ \ \ \ \ \ \ \ \ \text{Saccharic acid}\ \ \ \ \ \ \ \text{Gluconic acid}$

Strong oxidising agents like nitric acid oxidises both the terminal -CHO and -CH₂OH groups of glucose to give the dibasic acid, saccharic acid.

3. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

4. (d) Assertion is wrong statement but reason is correct statement.

Explanation:

If a certain compound gives negative test with ninhydrin and positive test with Benedict's solution then the compound should be a monosaccharide.

5.  (d) Assertion is wrong statement but reason is correct statement.

Explanation:

The rapid interconversion of $\alpha$-Dvgfucose and $\beta$-D-glucose in solution is known as mutarotation. Sugar gets hydrolysed with mineral acids.

$\text{C}_{12}\text{H}-{22}+\text{H}_2\text{O}\xrightarrow{\text{H}^+}\text{C}_6\text{H}_{12}\text{O}_6+\text{C}_6\text{H}_{12}\text{O}_6\\\ \ \ \ \text{Sugar}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Glucose}\ \ \ \ \ \text{Fructose}$

1. (a) X > Z > Y

Explanation:

Carboxytic acids are stronger acids than $-\stackrel{{+}}{\hbox{N}}\text{H}_3,$ therefore X is the strongest acid. Since –COOH has -I effect which decreases with distance therefore, effect is more pronounced on Z than on Y.

As a result Z is more acidic than Y, therefore, overall order of increasing acid strength is X > Z > Y.

2. (d) $\text{H}_3\stackrel{{+}}{\hbox{N}}\text{CHRCOO}^-$

Explanation:

In aqueous solutions, amino acids mostly exist as zwitter ion or dipolar ion.

$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{R}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\stackrel{{+}}{\hbox{N}}\text{H}_3-\text{CH}-\text{COO}^-\\\ \ \ \ \ \ \ \ \ \ \text{Zwitter ion}$

3. (c) At their isoelectric points.

Explanation:

Amino acids are least soluble at their isoelectric points. At a specific pH, called isoelectric point, the positive and negative charges balance each other and the net charge becomes zero. If there is a charge, the amino acid prefers to interact with water, rather than other amino acid molecules, this charge makes it more soluble.

4. (c) 6.0

Explanation:

$\text{Isoelectric point}=\frac{2.3+9.7}{2}=6$

5. (a) Glu-Cys-Gly

Explanation:

Since the tripeptide on hydrolysis gave two dipeptides Glu-Cys and Cys-Gly, hence, cysteine must be in between glutamic acid and glycine as given below:

$\ \ \ \ \ \ \ \ \ \text{CH}_2\text{CH}_2\text{COOH}\\\ \ \ \ \ \ \ \ \ \ |\\\stackrel{{+}}{\hbox{N}}\text{H}_3\text{CH}-\text{C}-\text{NHCH}-\text{CNHCH}_2\text{CO}^-\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\ \ \ \ \ \ \ \ \ \ \ \ |\ \ \ \ \ \ \ \ \ ||\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\ \ \ \ \ \ \text{HSCH}_2\ \ \text{O}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Glu-Cys-Gly}$