The reaction of the given compound \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}\) with HBr yields (a) \(\mathrm{CH}_{3}-\mathrm{CHBr} \mathrm{CH}_{2}\) (b) \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{CHBr}-\) (c) \(\mathrm{CH}_{3}-\mathrm{CHBrCH}_{2}-\) (d) \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{CHBr}-\)

In organic chemistry, an addition reaction is one of the most fundamental types of chemical reactions. It involves two or more molecules combining to form a larger molecule. Specifically, in the case of alkenes, which are hydrocarbons with a carbon-carbon double bond, an addition reaction can occur when a reactive substance, such as hydrogen bromide (HBr), interacts with this double bond.

During the reaction, the pi bond of the double bond is broken and new sigma bonds are formed with the atoms that were contained in the reactive substance. This leads to the addition of these atoms across the double bond. An important aspect of these reactions is that they are typically exothermic, meaning they release energy, and they usually proceed quite rapidly, which is why they're frequently encountered in industrial processes and synthetic pathways in the laboratory.

Another feature to remember is regioselectivity, which refers to the preference for the formation of one structural isomer over another when several isomers are possible products in a chemical reaction. This concept is key to predicting the outcome of many addition reactions, including those involving alkenes and HBr.

The specific type of addition reaction we are looking at is the reaction between an alkene and hydrogen bromide (HBr). When an alkene reacts with HBr, the hydrogen (H) atom and the bromine (Br) atom will add across the carbons that were previously connected by a double bond. This reaction is not only a classic example of an addition reaction but also illustrates the principle of Markovnikov's rule in action.

Hydrogen bromide is a hydrogen halide and acts as an electrophile due to the polar bond between hydrogen and bromine; bromine is more electronegative and carries a partial negative charge, while hydrogen has a partial positive charge. When an alkene encounters HBr, the electron-rich double bond is attracted to the partially positive hydrogen, leading to the initial formation of a carbocation intermediate. The bromide ion then quickly attacks the positively charged carbon, resulting in the addition of bromine to one carbon and hydrogen to the other. The outcome is specifically dictated by Markovnikov's rule, which is crucial for predicting which carbon bromine will attach to in our given exercise.

Organic chemistry concepts are integral to understanding the behavior of organic molecules in chemical reactions. Fundamental concepts such as bond polarity, electrophiles and nucleophiles, carbocations, and stereochemistry play pivotal roles in predicting reaction mechanisms and outcomes.

Markovnikov's Rule

Markovnikov's rule is a perfect illustration of how these concepts interplay. When we apply this rule to the addition of HBr to an alkene, we integrate the concept of bond polarity (HBr bond), reactants' reactivity (electrophilic H and nucleophilic alkene), and the carbocation stability (more substituted carbons form more stable carbocations). Furthermore, this rule helps us predict the position at which the bromine atom will add to the alkene, which ultimately dictates the structure of the resulting product.

Predicting the correct product in our exercise hinges upon applying these organic chemistry concepts and recognizing the governing rules like Markovnikov's rule to understand reaction outcomes thoroughly. This kind of problem-solving is at the heart of organic synthesis and is essential for the development of pharmaceuticals, polymers, and many other chemicals used in various industries.