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A key characteristic that distinguishes the respiratory pathway as amphibolic is that its intermediates:
The NCERT states: 'the carbon skeleton produced during respiration is used as precursors for biosynthesis of other molecules in the cell.' This highlights the anabolic role of respiratory intermediates, making the pathway amphibolic.
Why is it inaccurate to purely label the respiratory pathway as 'catabolic'?
The NCERT explicitly questions this understanding: 'But is this understanding correct? We have discussed above, at which points in the respiratory pathway different substrates would enter if they were to be respired... What is important to recognise is that it is these very compounds that would be withdrawn from the respiratory pathway for the synthesis of the said substrates.' This demonstrates its amphibolic nature.
When carbohydrates are used as a respiratory substrate, they are typically first converted into:
The NCERT states: 'Glucose is the favoured substrate for respiration. All carbohydrates are usually first converted into glucose before they are used for respiration.'
The interrelationship among metabolic pathways showing respiration-mediated breakdown of different organic molecules to CO2 and H2O (Figure 12.6, not provided here but referred to in text) visually represents:
Given the discussion of respiration as an amphibolic pathway and the description of various substrates entering at different points, the figure would illustrate how these pathways converge and diverge, supporting both breakdown and synthesis, hence its amphibolic nature.
Which of the following methods can be used to prepare carboxylic acids from alkyl halides with an increased carbon chain length?
The NCERT text states: 'The above methods (Grignard reagents and nitriles from alkyl halides) are useful for converting alkyl halides into corresponding carboxylic acids having one carbon atom more than that present in alkyl halides (ascending the series).'
An aromatic carboxylic acid can be prepared by the side-chain oxidation of which of the following compounds?
The NCERT text mentions: 'Aromatic carboxylic acids are also prepared by side-chain oxidation of alkylbenzenes.' And 'Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate.'
Which of the following starting materials will yield butanoic acid upon appropriate treatment?
The NCERT states: 'Primary alcohols are readily oxidised to carboxylic acids with common oxidising agents such as potassium permanganate ($KMnO_4$) in neutral, acidic or alkaline media or by potassium dichromate ($K_2Cr_2O_7$) and chromium trioxide ($CrO_3$) in acidic media (Jones reagent).' Using $K_2Cr_2O_7/H^+$ on Butan-1-ol will oxidize it to Butanoic acid. While Butyronitrile hydrolysis will give butanoic acid, option o1 is a direct method mentioned in the text for converting alcohol to acid, which is specifically highlighted with an example (Butan-1-ol to butanoic acid).
Which of the following Grignard reagents, when treated with carbon dioxide followed by acidification, will produce 2-phenylethanoic acid?
The reaction of Grignard reagents with carbon dioxide (dry ice) forms salts of carboxylic acids, which upon acidification, yield the carboxylic acid. To form 2-phenylethanoic acid ($C_6H_5CH_2COOH$), the Grignard reagent must be Benzylmagnesium bromide ($C_6H_5CH_2MgBr$). This allows for the addition of one carbon atom to the benzyl group.
Consider the following reaction sequence: R–X $\xrightarrow{\text{KCN}}$ A $\xrightarrow{\text{Hydrolysis, } H^+}$ B. If R-X is bromoethane, what is the final product B?
Bromoethane ($CH_3CH_2Br$) reacts with KCN to form ethyl nitrile ($CH_3CH_2CN$). Hydrolysis of nitriles ($CH_3CH_2CN$) in the presence of $H^+$ catalyst yields carboxylic acids. In this case, ethyl nitrile will be hydrolyzed to propanoic acid ($CH_3CH_2COOH$). The method from nitriles increases the carbon chain by one.
Which of the following statements about the preparation of carboxylic acids is INCORRECT?
The NCERT states: 'Primary and secondary alkyl groups are oxidised in this manner while tertiary group is not affected.' referring to the vigorous oxidation of alkylbenzenes to aromatic carboxylic acids. Therefore, tertiary alkylbenzenes are not readily oxidized.
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