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Organic Chemistry

102 questions

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Question 101Question →

Arrange the following organic compounds in order of INCREASING solubility in water, starting with the least soluble compound:

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Answer

The correct sequence from least soluble to most soluble in water is: Pentane, Pentan-1-ol, Butane-1,4-diol, Ethane-1,2-diol.
Water solubility in organic compounds is determined by the balance between hydrophilic (water-attracting) functional groups and hydrophobic (water-repelling) carbon chains. Pentane is non-polar and cannot form hydrogen bonds, making it the least soluble. Pentan-1-ol has one −OH-\text{OH} group but a large 5-carbon hydrophobic chain, giving it low solubility. Butane-1,4-diol contains two −OH-\text{OH} groups, significantly enhancing hydrogen bonding with water molecules. Ethane-1,2-diol has two −OH-\text{OH} groups and the shortest hydrophobic carbon chain (2 carbons), making it the most soluble in water.

Step-by-Step Solution

1
Analyze the functional groups present in each compound.
Pentane has no polar functional groups. Pentan-1-ol has one −OH-\text{OH} group. Butane-1,4-diol has two −OH-\text{OH} groups. Ethane-1,2-diol has two −OH-\text{OH} groups.
Water is a polar solvent that dissolves compounds capable of forming hydrogen bonds through polar functional groups like −OH-\text{OH}.
2
Compare the hydrophobic alkyl chain lengths for compounds with the same functional group capability.
Ethane-1,2-diol has a smaller non-polar carbon chain (2 carbons) compared to Butane-1,4-diol (4 carbons).
A larger non-polar alkyl region increases hydrophobic interaction, reducing solubility in water.
3
Establish the complete order of increasing solubility.
Pentane < Pentan-1-ol < Butane-1,4-diol < Ethane-1,2-diol.
Solubility increases with an increasing ratio of hydrophilic functional groups (−OH-\text{OH}) to non-polar alkyl chain length.

Key Concept

Solubility of organic compounds based on functional group polarity and hydrophobic alkyl chain length
Question 102Question →

Match each polyfunctional organic compound listed on the left with its principal IUPAC functional group suffix on the right, based on IUPAC nomenclature priority rules.

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Items

HOCH2CH2COOH\text{HOCH}_2\text{CH}_2\text{COOH}
CH3COCH2CHO\text{CH}_3\text{COCH}_2\text{CHO}
CH3CH(OH)COCH3\text{CH}_3\text{CH(OH)COCH}_3
CH2=CHCH2OH\text{CH}_2=\text{CHCH}_2\text{OH}

Matches

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Answer

The correct pairings match HOCH2CH2COOH\text{HOCH}_2\text{CH}_2\text{COOH} with -oic acid, CH3COCH2CHO\text{CH}_3\text{COCH}_2\text{CHO} with -al, CH3CH(OH)COCH3\text{CH}_3\text{CH(OH)COCH}_3 with -one, and CH2=CHCH2OH\text{CH}_2=\text{CHCH}_2\text{OH} with -ol.
In IUPAC nomenclature for polyfunctional organic compounds, the principal functional group determines the ending suffix of the compound name. Carboxylic acid (−COOH-\text{COOH}) outranks alcohol (−OH-\text{OH}), giving -oic acid; aldehyde (−CHO-\text{CHO}) outranks ketone (−CO−-\text{CO}-), giving -al; ketone (−CO−-\text{CO}-) outranks alcohol (−OH-\text{OH}), giving -one; and alcohol (−OH-\text{OH}) outranks alkene (C=C\text{C}=\text{C}), giving -ol.

Step-by-Step Solution

1
Identify all functional groups present in each compound.
Compound 1 contains hydroxyl and carboxyl; Compound 2 contains ketone and aldehyde; Compound 3 contains hydroxyl and ketone; Compound 4 contains alkene and alcohol.
Identifying all present functional groups is necessary before applying priority rules.
2
Apply standard IUPAC functional group seniority order.
Priority order: Carboxylic acid (−COOH-\text{COOH}) > Aldehyde (−CHO-\text{CHO}) > Ketone (−CO−-\text{CO}-) > Alcohol (−OH-\text{OH}) > Alkene (C=C\text{C}=\text{C}).
The group with higher priority determines the principal suffix of the IUPAC name, while lower priority groups are named as prefixes.
3
Assign the principal suffix to each compound.
Compound 1 matches -oic acid, Compound 2 matches -al, Compound 3 matches -one, and Compound 4 matches -ol.
Matches each compound structure to its appropriate IUPAC ending based on priority.

Key Concept

IUPAC Functional Group Seniority Hierarchy
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