The number of primary alcohols and total possible alcohols for \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\) are respectively? (a) 4,7 (b) 3,6 (c) 4,8 (d) 3,5

Understanding the concept of structural isomers is vital in organic chemistry.
Isomers are molecules with the same molecular formula but different structural arrangements. In the context of alcohols like pentanol ((C_5H_12O)), isomers arise because the hydroxyl group (OH) can be attached to different carbon atoms within the molecule.

With primary alcohols, the hydroxyl group is connected to a primary carbon, which itself is bonded to only one other carbon atom. If you were to consider placing the OH group on different carbon atoms in the chain, you'd end up with different substances, despite having the same formula. These substances would have different physical and chemical properties which is what makes isomerism such an interesting study in organic chemistry.

Secondary and tertiary alcohols are also part of the isomer family, with the hydroxyl group being bonded to carbons with more connections to other carbons, which we'll discuss further in later sections. For (C_5H_12O), specifically, the task is to discern and count all these variations, thereby unveiling the rich variety of isomers possible from a seemingly simple formula.

The hydroxyl group is fundamental to an alcohol's identity. It consists of an oxygen atom bound to a hydrogen atom ((OH)).
When attached to a carbon within an organic compound, it bestows the molecule with distinct 'alcohol' characteristics. The position where this hydroxyl group attaches hugely influences the nature of the alcohol, segregating them into primary, secondary, or tertiary classes.

In primary alcohols, the hydroxyl group is connected to a primary carbon, influencing properties like boiling point, solubility, and reactivity. For example, primary alcohols tend to have higher boiling points as they form strong intermolecular hydrogen bonds due to the accessible -OH group on a terminal carbon atom.

The placement of the -OH group defines the functional capabilities of the alcohol, dictating its behavior in chemical reactions such as oxidation or substitution. This versatility makes studying the hydroxyl group indispensable for students trying to comprehend organic chemistry's complexities.

Secondary and tertiary alcohols expand the diversity in the alcohol family. These alcohols are classified based on which carbon the hydroxyl group is attached to.
Secondary alcohols have the (OH) group on a carbon atom that is connected to two other carbons. These alcohols generally have moderate boiling points and are less reactive towards oxidation than primary alcohols.

Tertiary alcohols, on the other hand, feature the hydroxyl group attached to a carbon that is connected to three other carbon atoms. These are typically more sterically hindered, which impacts their chemical reactions. For instance, tertiary alcohols resist oxidation but may undergo other types of reactions, such as elimination.

In our exercise with (C_5H_12O), correctly identifying these alcohols—like 2-pentanol (secondary) and 2-methyl-2-butanol (which can be considered both secondary and tertiary due to tautomerism)—is crucial to count the correct number of isomers. This step highlights the importance of understanding the structural differences between secondary and tertiary alcohols to comprehensively grasp the scope of isomerism within organic compounds.