List all the possible products for each alkane substitution reaction. (Assume monosubstitution.) \begin{equation}\begin{array}{l}{\text { a. } \mathrm{CH}_{4}+\mathrm{Cl}_{2} \longrightarrow} \\ {\text { b. } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}+\mathrm{Br}_{2} \longrightarrow} \\ {\text { c. } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}+\mathrm{Cl}_{2} \longrightarrow} \\ {\text { d. } \mathrm{CH}_{3} \mathrm{CHBr}_{2}+\mathrm{Br}_{2} \longrightarrow}\end{array}\end{equation}

Chemical reactions are fundamental processes in which substances, known as reactants, transform into new substances, called products. These transformations occur through the breaking and forming of chemical bonds, which involves the rearrangement of atoms and often results in changes in energy. In the context of organic chemistry, the type of chemical reaction showcased in the exercise is known as a monosubstitution reaction.

This type of reaction is characterized by the exchange of a single atom or group within a molecule for another. Specifically, in an alkane monosubstitution reaction, an alkane, which is a hydrocarbon with single bonds only, reacts with a halogen to substitute one hydrogen atom with a halogen atom. Understanding this fundamental process is crucial not only in organic synthesis but also in industrial applications and biological systems where such reactions occur.

Organic chemistry is the branch of chemistry that deals with the study of the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. Alkanes, the simplest type of organic compounds, are composed only of carbon and hydrogen atoms connected by single bonds, forming a saturated hydrocarbon. As seen in the exercise, alkanes can undergo a variety of reactions, including monosubstitution reactions, which are integral for creating a diverse array of more complex molecules.

Understanding the reactivity of different types of carbon atoms within alkanes is key to predicting the outcome of these reactions; primary carbons are those bound to only one other carbon, secondary carbons to two other carbons, and tertiary to three. Each type offers different reactive sites for substitution, affecting the final product's structure. Hence, gaining proficiency in organic chemistry involves mastering such concepts to design synthesis pathways and to predict reaction outcomes effectively.

Halogenation is a specific type of chemical reaction where a halogen atom is introduced into an organic molecule. Halogens are elements found in group 17 of the periodic table, including fluorine, chlorine, bromine, and iodine. In the exercises provided, halogenation involves the substitution of a hydrogen atom in an alkane for a halogen atom.

This reaction is typically initiated by light or heat, causing the halogen to form radicals - highly reactive species with unpaired electrons. Once formed, these radicals can react with an alkane to replace one of its hydrogen atoms. For example, in methane (CH₄), chlorination yields chloromethane and hydrochloric acid. Notably, halogenation is not only an essential reaction for creating many chemical products but is also a topic covered extensively in organic chemistry courses. Students are expected to understand the mechanism behind it, the conditions under which it occurs, and the factors influencing the distribution of products formed during the reaction.