The extent of π electron conjugation in macrocyclic rings of (i) heme, (ii) coenzyme B12 and (iii) chlorophyll follows the order:a)(i) > (iii) > (ii)b)(i) > (ii) > (iii)c)(iii) > (i) > (ii)d)(ii) ≈ (i) > (iii)Correct answer is option 'A'. Can you explain this answer?

Question

The extent of &#960; electron conjugation in macrocyclic rings of (i) heme, (ii) coenzyme B12 and (iii) chlorophyll follows the order:a)(i) &#62; (iii) &#62; (ii)b)(i) &#62; (ii) &#62; (iii)c)(iii) &#62; (i) &#62; (ii)d)(ii) &#8776; (i) &#62; (iii)Correct answer is option 'A'. Can you explain this answer?

Answer

Heme have a phorphyring which have 11 conjugated bonds.... Coenzyme B12 have corin ring which have 6 conjugated bonds while chlorophyll have chlorine ring which have 10 conjugated bonds.. ... So extent of conjugation is directly proportional to the no of double bonds.. So order will be 1>3>2

Answer

Explanation:

The extent of electron conjugation in macrocyclic rings can be determined by analyzing the aromaticity and the delocalization of electrons within the ring system. In this case, we are comparing the extent of electron conjugation in the macrocyclic rings of heme, coenzyme B12, and chlorophyll.

I. Heme:

Heme is a macrocyclic ring structure that consists of four pyrrole rings linked together by methene bridges. The central iron atom in heme is coordinated by a histidine residue, forming a porphyrin complex. The conjugated system of double bonds in the pyrrole rings gives heme its characteristic color and is responsible for its ability to bind and transport oxygen in hemoglobin.

II. Coenzyme B12:

Coenzyme B12, also known as cobalamin, is a macrocyclic ring structure that contains a cobalt ion at its center. The cobalt ion is coordinated by a dimethylbenzimidazole group and a 5,6-dimethylbenzimidazole group. The macrocyclic ring of coenzyme B12 contains multiple double bonds, which contribute to its redox properties and its role as a cofactor in enzymatic reactions.

III. Chlorophyll:

Chlorophyll is a macrocyclic ring structure that is responsible for the absorption of light in photosynthetic organisms. It consists of a porphyrin ring system with a magnesium ion at its center. The conjugated system of double bonds in the porphyrin ring allows chlorophyll to absorb light energy and transfer it to other molecules in the photosynthetic process.

Extent of Electron Conjugation:

Based on the structures and properties of heme, coenzyme B12, and chlorophyll, the extent of electron conjugation in their macrocyclic rings can be determined as follows:

(i) Heme: Heme has a highly conjugated system of double bonds due to the presence of four pyrrole rings. The delocalization of electrons in the conjugated system makes heme aromatic and highly conjugated.

(ii) Coenzyme B12: Coenzyme B12 also has a conjugated system of double bonds in its macrocyclic ring. However, the presence of the cobalt ion at the center of the ring disrupts the delocalization of electrons to some extent. Therefore, the extent of electron conjugation in coenzyme B12 is lower than that in heme.

(iii) Chlorophyll: Chlorophyll has a similar macrocyclic ring structure to heme, with a porphyrin ring and a central metal ion (magnesium). The conjugated system of double bonds in the porphyrin ring allows for a high extent of electron conjugation, making chlorophyll highly conjugated.

Conclusion:

Based on the extent of electron conjugation in their macrocyclic rings, the correct order is:

a) (i) Heme, (iii) Chlorophyll, (ii) Coenzyme B

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