Question

Which of the following compounds are alcohols? (a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) (e) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\)

Short answer

The compounds (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and (c) \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}\) are the alcohols.

Step-by-step solution

Identify the compounds containing the hydroxyl group

Look at each compound in the list and find where a hydroxyl group (OH) is attached to a carbon (C) atom. After successfully identifying them, you can be sure that these compounds are alcohols.

Analysis of Compound (a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\)

In this compound, a methoxy group (OCH3) is attached to a methyl group (CH3). It doesn't contain a hydroxyl group (OH) directly attached to a carbon atom, so it isn't an alcohol.

Analysis of Compound (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)

In this compound, a hydroxyl group (OH) is directly attached to a carbon atom which forms Ethanol (a type of alcohol). Therefore, this compound is an alcohol.

Analysis of Compound (c) \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}\)

Here, the hydroxyl group (OH) is directly attached to a carbon atom which forms Propan-2-ol (a type of alcohol). Thus, this compound is an alcohol.

Analysis of Compound (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\)

This compound is an organic compound, but the oxygen atom is double bonded to a carbon atom in a carbonyl group (CO), not a hydroxyl group (OH). Therefore, it is not an alcohol.

Analysis of Compound (e) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\)

Similar to (d), in this case, the oxygen atom is part of a carbonyl group (CHO) which is not the same as a hydroxyl group (OH). Therefore, it is not an alcohol.

Key concepts

Hydroxyl Group

Understanding the hydroxyl group is fundamental in identifying alcohols in organic chemistry. A hydroxyl group consists of one oxygen atom covalently bonded to one hydrogen atom, represented by the chemical notation -OH. When this group is bonded to a saturated carbon atom (one that has single bonds with other atoms), it forms an alcohol functional group.

In organic compounds, the presence of a hydroxyl group is the key distinguishing feature of alcohols. Its unique structural composition allows it to engage in hydrogen bonding, which has significant implications on the physical properties of the alcohol, like higher boiling and melting points compared to similar-sized molecules without the hydroxyl group.

Identifying a hydroxyl group involves looking for the -OH group bonded to a carbon atom in the compound's structure. It is essential not to confuse it with other oxygen-containing groups such as ethers (R-O-R') or ketones (R-CO-R'), which can look similar but possess different properties and reactivities.

Organic Chemistry

The field of organic chemistry is vast, dealing with the structure, properties, composition, reactions, and preparation of carbon-containing compounds. These include not only hydrocarbons but also compounds with any number of other elements, including hydrogen (most compounds contain at least one carbon–hydrogen bond), nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur.

This branch of chemistry is instrumental in studying life's molecular basis and has applications in areas such as pharmaceuticals, petrochemicals, food, explosives, and plastics. When identifying alcohols, organic chemistry provides a system of nomenclature and a framework for understanding how the molecules will interact with other substances based on their functional groups, like the hydroxyl group in alcohols.

Organic chemists use various analytical techniques to determine the structure of compounds, including spectroscopy and crystallography. These techniques help to confirm the presence or absence of particular functional groups such as the hydroxyl group in alcohols.

Alcohol Functional Group

The alcohol functional group is critical in organic molecules and can significantly alter a compound's physical and chemical properties. This group features a hydroxyl group bonded to a carbon atom. In the simplest form, the alcohol functional group is represented as R-OH, where R is the rest of the molecule.

Alcohols are classified based on the carbon to which the hydroxyl group is attached. If it's attached to a primary carbon (connected to only one other carbon), the alcohol is referred to as a primary alcohol. Secondary (attached to two carbons) and tertiary alcohols (attached to three carbons) follow a similar logic.

Alcohols play a significant role in pharmaceuticals, antiseptics, fuels, and solvents, due to their reactivity and solubility. When identifying alcohols, it is crucial to note the hydroxyl group's position, as it determines the alcohol's reactivity and classification. The nature of the carbon chain (R) attached to the hydroxyl group also affects the alcohol's solubility and boiling point, influencing its application in various industries.