If a compound is reduced, what is the result?
Fewer C-H bonds
Increased number of C-H bonds
Fewer C-Z bonds
Both increased number of C-H bonds and fewer C-Z bonds
The Correct Answer and Explanation is:
The correct answer is:
Both increased number of C-H bonds and fewer C-Z bonds
In chemistry, reduction refers to a process in which a molecule, atom, or ion gains electrons or undergoes a decrease in its oxidation state. In organic chemistry, however, the definition of reduction can be extended beyond just electron gain—it also includes specific structural changes in a molecule, especially concerning carbon-hydrogen (C-H) and carbon-heteroatom (C-Z) bonds, where Z represents a more electronegative element (e.g., O, N, X such as halogens).
Let’s break this down into the two parts of the correct answer:
1. Increased Number of C-H Bonds
One key indicator of reduction in organic compounds is the increase in the number of hydrogen atoms bonded to carbon. This means forming more C-H bonds. For example:
- When alkenes (C=C) are reduced to alkanes (C-C) via hydrogenation, two new C-H bonds are formed.
- Similarly, the reduction of carbonyl compounds like ketones or aldehydes to alcohols increases the number of C-H bonds.
This increase in C-H bonds means that the carbon is gaining hydrogen, which corresponds to a gain of electrons, fulfilling the fundamental definition of reduction.
2. Fewer C-Z Bonds
Reduction also commonly involves the loss of bonds to more electronegative atoms, such as oxygen, nitrogen, or halogens. These are known as C-Z bonds:
- For instance, the reduction of a carboxylic acid (-COOH) to a primary alcohol (-CH₂OH) involves the removal of a double bond to oxygen and replacement with hydrogen atoms.
- This results in fewer C-O or C-Cl bonds, which are associated with oxidation due to the withdrawal of electron density by electronegative atoms.
Thus, losing C-Z bonds (where Z is an electronegative atom) is another hallmark of reduction.
Conclusion:
Both the increase in C-H bonds and the decrease in C-Z bonds reflect the movement of electron density toward the carbon atom, which constitutes reduction in an organic context. Therefore, “Both increased number of C-H bonds and fewer C-Z bonds” is the most comprehensive and correct answer.
