Question

Draw structures corresponding to the following names: (a) Octanal (b) Methyl phenyl ketone (c) 4-Methylhexanal (d) Methyl tert-butyl ketone

Short answer

Draw structures for octanal, acetophenone, 4-methylhexanal, and pinacolone.

Step-by-step solution

Understanding Octanal

Octanal is an aldehyde with eight carbon atoms. The suffix '-al' indicates an aldehyde group is present. The formula is CH3(CH2)6CHO. Draw a chain of eight carbon atoms, ensuring the terminal carbon is a part of the aldehyde group (CHO), thus marking the end of the chain.

Drawing Octanal

Starting from left to right, draw a straight chain of eight carbon atoms. Attach a double-bonded oxygen and a hydrogen to the terminal carbon on the right to form the aldehyde group.

Understanding Methyl Phenyl Ketone

Methyl phenyl ketone is a ketone known as acetophenone. It has a phenyl group (C6H5) and a methyl group (CH3) attached to the carbonyl carbon (C=O). The structure is C6H5COCH3.

Drawing Methyl Phenyl Ketone

Draw a benzene ring to represent the phenyl group. Attach a carbon with a double-bonded oxygen (CO) to one carbon of the benzene. Then add a methyl group (CH3) to the other side of the carbonyl carbon.

Understanding 4-Methylhexanal

4-Methylhexanal is a six-carbon aldehyde with a methyl group on the fourth carbon. The aldehyde group is at the end of the chain. Its formula is CH3CH2CH(CH3)CH2CH2CHO.

Drawing 4-Methylhexanal

Draw a chain of six carbon atoms for hexanal. Starting from the left (or any direction), place the aldehyde group (CHO) at the right end. Then, add a methyl group (CH3) to the fourth carbon in the chain, counting from the aldehyde end.

Understanding Methyl Tert-Butyl Ketone

Methyl tert-butyl ketone, also called pinacolone, is a ketone with a tert-butyl (t-Bu) group and a methyl group attached to a central carbonyl carbon. The structure is (CH3)3C-C(O)-CH3.

Drawing Methyl Tert-Butyl Ketone

Draw a central carbon with a double-bonded oxygen above or below it. Attach a tert-butyl group [(CH3)3C] to one side and a methyl group (CH3) to the other.

Key concepts

Aldehydes

Aldehydes are an essential class of organic compounds. They feature a functional group characterized by a carbon atom double-bonded to an oxygen atom (C=O), known as the carbonyl group. What sets aldehydes apart is the presence of a hydrogen atom attached to this carbonyl carbon, forming the functional group R-CHO, where R represents any generic alkyl or aryl group.

Key traits of aldehydes include:

• A characteristic smell, varying from pleasant (e.g., vanillin) to pungent (e.g., formaldehyde).
• The occurrence of the carbonyl group at the end of the carbon chain enhances their reactivity compared to ketones.
• Widespread use in the production of fragrances, flavorings, and plastics.

When drawing aldehyde structures, like octanal and 4-methylhexanal, the carbonyl group always appears at the terminal carbon. This unique positioning is crucial in determining both reactivity and nomenclature.

Ketones

Ketones are another pivotal group of organic compounds characterized by a carbonyl group. However, unlike aldehydes, the carbonyl group in ketones is flanked by two carbon-containing groups, which can be either alkyl or aryl groups. This gives ketones a general formula of R-CO-R', where R and R' denote the carbon groups.

Some defining attributes of ketones include:

• Keto group located within the carbon chain, making their reactivity less than that of aldehydes.
• Common usage in industrial applications, like solvents, and within the human body as metabolic products.
• Lacking the prominent and often potent odors that aldehydes possess.

When constructing ketone structures, as seen in methyl phenyl ketone and methyl tert-butyl ketone, the carbonyl group is always part of the internal carbon atoms, ensuring that it's surrounded by other carbon groups, offering stability to the structure.

Structural Formulas

Understanding structural formulas is vital for representing organic compounds clearly and accurately. These diagrams depict the arrangement of atoms in a molecule and demonstrate how they connect.

Key aspects of drawing structural formulas include:

• Display all carbon-to-carbon bonds to make the molecule's shape evident.
• Highlight functional groups distinctly, like the carbonyl group in aldehydes and ketones.
• Show hydrogen atoms explicitly when needed, especially in smaller compounds.

While using structural formulas for compounds like aldehydes and ketones, ensure the distinct arrangement of the functional group is emphasized. For example, in octanal, the aldehyde group clearly situates at the terminal carbon, whereas, in pinacolone, the ketone group is centrally placed within the chain.

IUPAC Nomenclature

The IUPAC nomenclature is an internationally agreed system to name organic compounds. It ensures that each compound's name accurately describes its structure, with rules specifying how to name different functional groups and branches.

Important features of the IUPAC naming system:

• Identify the longest carbon chain containing the principal functional group.
• Name and number the chain in a way that gives the smallest number to the primary functional group, such as the aldehyde or ketone group.
• Use prefixes for substituent groups (like methyl, phenyl) and position them based on their location in the carbon chain.

For example, in 4-methylhexanal, 'hexanal' denotes a six-carbon aldehyde, and '4-methyl' specifies a methyl group on the fourth carbon. This systematic approach serves to provide a clear, universally understood description of complex molecules.