NESA Chemistry Nomenclature

Methyl pentanoate contains 6 carbons ($1$ from methyl + $5$ from pentanoate), whereas propyl butanoate contains 7 carbons ($3$ from propyl + $4$ from butanoate). Isomers must have the same molecular formula.

This name is invalid because a pentanoic acid chain only has 5 carbons, so a substituent cannot be at position 6. Furthermore, a methyl pentanoic acid derivative would only have 6 carbons total, not the required 7.

Although a structure constructed from this name would have 7 carbons, '3-propylbutanoic acid' is not a valid IUPAC name. The propyl group would extend the longest carbon chain, making the correct parent name hexanoic acid (specifically 3-methylhexanoic acid).

Incorrect. There are more than 2 structural isomers; this answer likely only accounts for the geminal isomers (both fluorines on the same carbon).

Incorrect. There are more than 3 structural isomers; this answer likely misses one of the possible arrangements, such as 1,3-difluoropropane.

Incorrect. There are only 4 unique structural isomers; any fifth arrangement would just be a duplicate of one of the four due to the symmetry of the propane chain.

Incorrect. There is more than one unique position on a straight four-carbon chain where the bromine atom can be attached.

Incorrect. Attaching the bromine to the third carbon simply creates 2-bromobutane again, just numbered from the opposite end of the chain.

Incorrect. While there are four total structural isomers for $C_4H_9Br$, two of them have branched carbon chains (1-bromo-2-methylpropane and 2-bromo-2-methylpropane), leaving only two straight-chain isomers.

Incorrect. This underestimates the number of isomers. The fluorine atoms can be arranged on the same carbon or different carbons, creating multiple isomers.

Incorrect. This only accounts for the two structural isomers (1,1-difluoroethene and 1,2-difluoroethene) but misses the geometric (cis-trans) isomers of 1,2-difluoroethene.

Incorrect. This overestimates the number of isomers. Only three distinct structural and geometric arrangements are possible for $\text{C}_2\text{H}_2\text{F}_2$.

There are actually four structural isomers of $\text{C}_5\text{H}_{10}\text{O}$ that are aldehydes: pentanal, 2-methylbutanal, 3-methylbutanal, and 2,2-dimethylpropanal.

There are no isomers with an ethyl side branch. If you try to place an ethyl group on a 3-carbon aldehyde chain, the longest chain containing the aldehyde group becomes 4 carbons long, making it a methyl branch instead (e.g., 2-methylbutanal).

By definition, the aldehyde functional group (-CHO) is always located at the end of the carbon chain, which is designated as the first carbon atom (C1), not the second.

This is incorrect because there are more than 4 structural isomers. This answer likely misses one of the positional combinations of the halogens on the propane chain.

This is incorrect because it overcounts the number of structural isomers. There are exactly 5 unique positional combinations for one bromine and one chlorine atom on a propane chain.

This is incorrect because it overcounts the number of structural isomers. Stereoisomers (enantiomers) are not counted when specifically asking for structural isomers.

Polyesters are polymers made of repeating ester linkages, not individual molecules containing both amine and carboxylic acid groups on the same carbon.

Soaps are typically sodium or potassium salts of long-chain fatty acids and do not contain an amine group.

Biodiesel consists of mono-alkyl esters of long-chain fatty acids, which lack the amine group mentioned in the description.

The molecule $\text{CH}_2=\text{CBrCl}$ has two identical hydrogen atoms on one of the double-bonded carbons, which prevents cis-trans isomerism.

The molecule $\text{CH}_3\text{CHBrCl}$ is an alkane with only single bonds, so it cannot exhibit cis-trans isomerism (though it does have enantiomers).

The molecule $(\text{CH}_3)_2\text{C}=\text{CCl}_2$ has identical groups on both carbons of the double bond (two methyls on one, two chlorines on the other), making cis-trans isomerism impossible.

Isomers have the same molecular formula, meaning they contain the exact same types and numbers of atoms.

Isomers are defined by having different structural formulas (arrangements of atoms) despite having the same molecular formula.

Saturated hydrocarbons (alkanes) are generally stable and unreactive, so they do not react vigorously with one another.

This molecule contains a cyano group ($-CN$), making it a nitrile (specifically propanenitrile), not an amide.

This molecule contains an amino group ($-NH_2$) attached to an alkyl chain, identifying it as an amine (ethylamine). An amide requires a carbonyl group adjacent to the nitrogen.

This is an ammonium salt (ammonium acetate), composed of acetate ions and ammonium ions held together by ionic bonds, rather than the covalent carbonyl-nitrogen bond found in amides.

Since structural isomers share the same molecular formula, they contain the exact same number of atoms of each element and therefore have identical molar masses.

Molecular mass is determined by the sum of the atomic masses in the molecular formula; since isomers have the same formula, their molecular masses are the same.

The empirical formula represents the simplest ratio of elements; because the molecular formula is identical for isomers, their empirical formulas are also identical.

Incorrect. This structure represents 2-methylpent-2-ene, where the double bond is located between the second and third carbon atoms.

Incorrect. This structure represents 4-methylpent-1-ene, where the methyl group is attached to the fourth carbon atom instead of the second.

Incorrect. This structure represents 3-methylpent-1-ene, where the methyl group is attached to the third carbon atom.

Cyclohexane contains only C-C single bonds, whereas benzene has delocalized pi electrons resulting in a carbon-carbon bond order of 1.5, meaning their average bond strengths differ.

Cyclohexane is a cycloalkane (general formula $C_nH_{2n}$) while benzene is an aromatic hydrocarbon (general formula $C_nH_{2n-6}$), so they belong to different homologous series.

Carbon is a Group 14 element and always has exactly four valence electrons, regardless of the molecule it is part of.