Hexamethylbenzene undergoes free-radical chlorination to give one monochlorinated product (C12H17Cl) and four dichlorinated products (C12H16Cl2). These products are easily separated by GC-MS, but the dichlorinated products are difficult to distinguish by their mass spectra. Draw the monochlorinated product and the four dichlorinated products, and explain how 13C NMR would easily distinguish among these compounds.

Verified step by step guidance

1. Identify the structure of hexamethylbenzene, which is a benzene ring with six methyl groups attached to each carbon.
2. For the monochlorinated product, consider that chlorination will replace one hydrogen atom from one of the methyl groups, resulting in C12H17Cl.
3. For the dichlorinated products, consider that chlorination will replace two hydrogen atoms from the methyl groups. There are several possible combinations for this, leading to different isomers.
4. Draw the possible structures for the dichlorinated products: (1) two chlorines on the same methyl group, (2) chlorines on two adjacent methyl groups, (3) chlorines on two methyl groups separated by one carbon, and (4) chlorines on two methyl groups separated by two carbons.
5. Explain how 13C NMR can distinguish these compounds: Each unique carbon environment will give a distinct signal in the 13C NMR spectrum. The number and position of chlorines will affect the chemical shift and splitting pattern, allowing differentiation of the isomers.

Key Concepts

Free-Radical Chlorination

Free-radical chlorination is a reaction mechanism where chlorine reacts with alkanes or aromatic compounds in the presence of heat or light, leading to the formation of free radicals. This process involves three main steps: initiation, propagation, and termination. In the case of hexamethylbenzene, the chlorination results in the substitution of hydrogen atoms with chlorine, yielding various chlorinated products based on the positions of substitution.

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. In 13C NMR, the different chemical environments of carbon atoms in a molecule lead to distinct resonance signals. This allows for the identification of unique carbon environments in the monochlorinated and dichlorinated products of hexamethylbenzene, making it easier to distinguish between them based on their chemical shifts.

Isomerism in Chlorinated Products

Isomerism refers to the existence of compounds with the same molecular formula but different structural arrangements or spatial orientations. In the case of the dichlorinated products of hexamethylbenzene, the different positions of chlorine substitution lead to structural isomers. These isomers can exhibit varying physical and chemical properties, which can complicate their analysis by mass spectrometry, but can be effectively differentiated using 13C NMR due to their unique carbon environments.