What is the structural formula of methanal and methanone? Are their structures possible? What about ethanal and ethanone?
The correct answer and explanation is:
Structural Formulas:
- Methanal (Formaldehyde):
Structural formula: H–C(=O)–H
Methanal has one carbon atom bonded to two hydrogen atoms and double bonded to one oxygen atom. - Methanone:
Methanone refers to a ketone with one carbon atom. Ketones require a carbonyl group (C=O) bonded to two carbon atoms. Since methanone would have only one carbon atom, it cannot have two carbon groups attached to the carbonyl carbon. Therefore, methanone does not exist as a stable compound. - Ethanal (Acetaldehyde):
Structural formula: CH3–C(=O)–H
Ethanal has two carbon atoms. The first carbon (CH3) is bonded to the second carbon which is double bonded to oxygen (carbonyl) and also bonded to a hydrogen atom. - Ethanone (Acetone):
Structural formula: CH3–C(=O)–CH3
Ethanone is commonly called acetone. It has three carbon atoms in total, with the middle carbon double bonded to oxygen (carbonyl) and bonded to two methyl groups (CH3). This is a stable ketone.
Explanation:
Methanal is the simplest aldehyde, containing one carbon atom double bonded to oxygen and bonded to two hydrogens. Its structure is straightforward and stable because aldehydes require at least one hydrogen bonded to the carbonyl carbon.
Methanone, by contrast, is a theoretical ketone with only one carbon. Ketones need the carbonyl carbon to be bonded to two other carbon atoms, which is impossible with only one carbon in the molecule. Hence, methanone cannot exist because the carbonyl carbon cannot be bonded to two carbon substituents.
Ethanal is an aldehyde with two carbons. The carbonyl carbon is bonded to one hydrogen and one methyl group, fulfilling aldehyde requirements and making it a stable compound. It is commonly known as acetaldehyde and is widely used in chemical synthesis.
Ethanone, or acetone, is the simplest ketone with two methyl groups bonded to the carbonyl carbon. It has three carbons total, with the middle carbon double bonded to oxygen. This molecule is very stable and common as a solvent and chemical intermediate.
In summary, aldehydes like methanal and ethanal exist with a carbonyl carbon bonded to at least one hydrogen, while ketones require the carbonyl carbon bonded to two carbons, meaning methanone is impossible, but ethanone (acetone) is stable and common.