Understanding Alcohol Nomenclature

Alcohols are organic compounds containing a hydroxyl group (-OH) attached to a carbon atom. Their nomenclature involves using the IUPAC system and often includes common names. The IUPAC name is derived from the parent alkane by replacing the '-e' ending with '-ol'. The common name typically uses the alkyl group name followed by 'alcohol'.

Analyzing Molecular Formula, IUPAC Name, and Common Name Sets

We need to examine each given set of Molecular Formula, IUPAC Name, and Common Name to identify the incorrect one. Let's break down each option:

Option 1: C$_{2}$H$_{5}$OH - Ethanol - Ethyl Alcohol

• Molecular Formula: C$_{2}$H$_{5}$OH
• This formula represents an alcohol with two carbon atoms.
• IUPAC Name: Ethanol
• 'Eth-' indicates two carbon atoms. '-anol' indicates an alcohol. This matches the two-carbon formula.
• Common Name: Ethyl Alcohol
• 'Ethyl' is the alkyl group derived from ethane (two carbons). This matches the two-carbon alcohol.
• This set correctly matches the molecular formula, IUPAC name, and common name for a two-carbon alcohol.

Option 2: C$_{4}$H$_{9}$OH - Butanol - Butyl Alcohol

• Molecular Formula: C$_{4}$H$_{9}$OH
• This formula represents an alcohol with four carbon atoms.
• IUPAC Name: Butanol
• 'But-' indicates four carbon atoms. '-anol' indicates an alcohol. This matches the four-carbon formula. (Note: Butanol can refer to different isomers like butan-1-ol, butan-2-ol, etc., but 'Butanol' as a general name is acceptable here).
• Common Name: Butyl Alcohol
• 'Butyl' is the alkyl group derived from butane (four carbons). This matches the four-carbon alcohol. (Note: Similar to Butanol, there are different butyl groups, but 'Butyl Alcohol' as a general term is used).
• This set correctly matches the molecular formula, IUPAC name, and common name for a four-carbon alcohol.

Option 3: C$_{3}$H$_{7}$OH - Propanol - Propyl Alcohol

• Molecular Formula: C$_{3}$H$_{7}$OH
• This formula represents an alcohol with three carbon atoms.
• IUPAC Name: Propanol
• 'Prop-' indicates three carbon atoms. '-anol' indicates an alcohol. This matches the three-carbon formula. (Note: Propanol can refer to propan-1-ol or propan-2-ol).
• Common Name: Propyl Alcohol
• 'Propyl' is the alkyl group derived from propane (three carbons). This matches the three-carbon alcohol. (Note: Can be n-propyl or isopropyl).
• This set correctly matches the molecular formula, IUPAC name, and common name for a three-carbon alcohol.

Option 4: C$_{2}$H$_{3}$OH - Methanol - Methyl Alcohol

• Molecular Formula: C$_{2}$H$_{3}$OH
• This formula shows two carbon atoms (C$_{2}$).
• IUPAC Name: Methanol
• 'Meth-' indicates one carbon atom. This conflicts with the molecular formula C$_{2}$H$_{3}$OH which has two carbon atoms. The correct formula for methanol is CH$_{3}$OH.
• Common Name: Methyl Alcohol
• 'Methyl' corresponds to the alkyl group with one carbon atom (CH$_{3}$). This also conflicts with the molecular formula C$_{2}$H$_{3}$OH which has two carbon atoms. The correct formula for methyl alcohol is CH$_{3}$OH.
• Additionally, the formula C$_{2}$H$_{3}$OH itself suggests a degree of unsaturation (compared to a saturated 2-carbon alcohol, ethanol, C$_{2}$H$_{5}$OH). A common 2-carbon alcohol is Ethanol (Ethyl Alcohol), C$_{2}$H$_{5}$OH.
• This set incorrectly links a two-carbon-based formula (C$_{2}$H$_{3}$OH) with one-carbon-based names (Methanol, Methyl Alcohol).

Based on the analysis, the set presented in Option 4 contains incorrect associations between the molecular formula, IUPAC name, and common name.

Identifying the INCORRECT Set

Comparing the given options, Option 4 lists C$_{2}$H$_{3}$OH with Methanol and Methyl Alcohol. This is incorrect because Methanol and Methyl Alcohol are names for the one-carbon alcohol with the formula CH$_{3}$OH.

Revision Table: Common Alcohols

Additional Information on Alcohol Nomenclature

• The general formula for saturated monohydric alcohols (alcohols with one -OH group) is C$_{n}$H$_{2n+1}$OH or C$_{n}$H$_{2n+2}$O.
• The number of carbon atoms ('n') determines the root name (Meth-, Eth-, Prop-, But-, etc.).
• For alcohols with more than two carbon atoms, the position of the -OH group is specified in the IUPAC name (e.g., Propan-1-ol, Propan-2-ol). This detail is often omitted in simple questions for lower homologues but is crucial for higher ones.
• Common names are widely used, especially for simpler alcohols like methyl alcohol and ethyl alcohol.
• The molecular formula C$_{2}$H$_{3}$OH could potentially represent vinyl alcohol (ethenol), CH$_{2}$=CH-OH. However, vinyl alcohol is unstable and quickly isomerizes to acetaldehyde. Regardless, C$_{2}$H$_{3}$OH does not correspond to Methanol or Methyl Alcohol.