Quiz 3 - Introduction to Organic Chemistry | Introduction to Organic Chemistry

The chemical structure shown represents a naphthalene ring with two methyl groups (-CH₃) attached. The naphthalene ring itself consists of two fused benzene rings, with a molecular formula of C₁₀H₆​. Each methyl group (-CH₃) adds one carbon and three hydrogen atoms.

Therefore, the total molecular formula is: C₁₂H₁₂

An alkyne is a hydrocarbon that contains at least one carbon-carbon triple bond. The general formula for an alkyne is C_nH_2n−2​. For example:

• C₂H₂ is ethyne (acetylene),
• C₄H₆ is butyne.

The other options are:

• C₂H₄ (A) is ethene (an alkene),
• C₃H₆ (B) is propene (an alkene),
• C₃H₈ (C) is propane (an alkane).

There are 3 isomers of C₃H₈O:

• 1-Propanol (CH₃CH₂CH₂OH): The hydroxyl group (-OH) is attached to the first carbon in the chain.
• 2-Propanol (CH₃CH(OH)CH₃): The hydroxyl group (-OH) is attached to the second carbon in the chain.
• Methoxyethane (CH₃OCH₂CH₃): This is an ether where the oxygen atom is between two alkyl groups (CH₃ and C₂H₅).

The molecular formula of propene (C₃H₆) consists of 3 carbon atoms and 6 hydrogen atoms. Propene is an alkene with a double bond between two carbon atoms (CH₂CH$-$CH₃), which results in a total of 6 hydrogen atoms.

(A) CH₃COOCH₂CH₃ is an ester because it has the −COO− functional group, typical of esters.

(B) is a peroxide with an −O−O− bond, (C) is an ether, and (D) is a carboxylic acid due to the −COOH group.

1. The longest carbon chain that includes the double bond is a 5-carbon chain, making it a "pentene"
2. The double bond starts at the 2nd carbon, so the base name is "2-pentene"
3. There is a methyl group (CH₃) attached to the 4th carbon of the chain.

Therefore, the correct IUPAC name is 4-methyl-2-pentene.

A compound can exist in optically active forms (chirality) if it has a chiral center, which is a carbon atom bonded to four different groups. In this case: CH₃CH₂CH(OH)CH₃ has a carbon atom (the third carbon) bonded to a hydroxyl group (-OH), a methyl group (-CH₃), an ethyl group (-CH₂CH₃), and a hydrogen atom, making it a chiral center.

The other compounds do not have a carbon atom attached to four different groups, so they are not optically active.

The structure shown has a six-carbon chain (hexane) with a methyl group (-CH₃) attached to the third carbon. Thus, the correct IUPAC name is 3-methylhexane.

To determine how many different aldehydes with the molecular formula C₅H₁₀O are possible, we must consider all the possible structural isomers that can form an aldehyde group (-CHO) with a 5-carbon backbone. Aldehydes have the functional group (-CHO) at the end of the chain.

Here are the possible structures:

• Pentanal: normal chain, 5 carbons in a straight chain, CH₃(CH₂)₃CHO.
• 2-methylbutanal: 4-carbon chain with a methyl group on the second carbon, CH₃CH(CH₃)CH₂CHO.
• 3-methylbutanal: 4-carbon chain with a methyl group on the third carbon, CH₃CH₂CH(CH₃)CHO.
• 2,2-dimethylpropanal: 3-carbon chain with two methyl groups attached to the second carbon, (CH₃)₂CHCHO.

Both 2-chloropentane and 3-chloropentane have the same number of carbon atoms (5) and the same number of chlorine atoms (1). The only difference between the two is the position of the chlorine atom on the carbon chain:

• 2-chloropentane has the chlorine atom attached to the second carbon atom.
• 3-chloropentane has the chlorine atom attached to the third carbon atom.

The carbon chain remains the same in both cases, so the correct distinction is the position of the chlorine atom.