Question

Draw the structure for 2 -bromo- 2 -chloro-3-methylpentane, and indicate any chiral carbons in the molecule.

Short answer

The structure of 2-bromo-2-chloro-3-methylpentane is H3C-CH(Br)(Cl)-CH(CH3)-CH2-CH3. The second carbon atom in the molecule, \( \color{blue}{C} \) in H3C-\(\color{blue}{C}\)(Br)(Cl)-CH(CH3)-CH2-CH3, is chiral as it is bonded to four different groups (CH3, Br, Cl, and the rest of the chain).

Step-by-step solution

Understand the name of the compound

The given compound is 2-bromo-2-chloro-3-methylpentane. It is an organic compound with a pentane skeleton (5 carbon atoms). There are three substituents present in the compound: bromo, chloro, and methyl groups. The number before each substituent indicates the position of the substituent on the pentane chain. The structure will have a bromo group and a chloro group on the second carbon and a methyl group on the third carbon.

Draw the pentane skeleton

To draw the pentane skeleton, place five carbon atoms in a horizontal chain. Each carbon will have single bonds to each of its neighbors. Each carbon has a hydrogen atom bonded to it (not shown) to complete the bonding. The chain appears as follows: C-C-C-C-C

Add substituents to the pentane skeleton

Now, add the substituents to the pentane skeleton according to their positions in the name: - Place the bromo group (Br) on the second carbon atom - Place the chloro group (Cl) on the second carbon atom - Place the methyl group (CH3) on the third carbon atom The molecule now appears like this: H3C-CH(Br)(Cl)-CH(CH3)-CH2-CH3

Identify chiral carbons in the molecule

A chiral carbon atom in an organic compound is one that is bonded to four different groups or atoms. Since the second carbon is bonded to four different groups (CH3, Br, Cl, and the rest of the chain), this carbon is chiral: H3C-\(\color{blue}{C}\)(Br)(Cl)-CH(CH3)-CH2-CH3 In conclusion, the structure of 2-bromo-2-chloro-3-methylpentane is H3C-CH(Br)(Cl)-CH(CH3)-CH2-CH3. The second carbon atom in the molecule is chiral.

Key concepts

Understanding Chiral Carbons

A chiral carbon is a quintessential concept in organic chemistry that adds a layer of complexity to the structure and properties of organic molecules. It's defined by its unique feature of being attached to four different groups or atoms, creating a non-superimposable mirror image, much like one's left and right hands are mirror images but not identical. This attribute is also called 'stereocenter' or 'asymmetric carbon'.

While drawing organic structures, indicating chiral carbons can help decipher the molecule's three-dimensional layout. In the given exercise, the second carbon atom in 2-bromo-2-chloro-3-methylpentane is identified as chiral because it is connected to a hydrogen atom, a bromine atom, a chlorine atom, and a methylpentane chain. Recognizing these centers is crucial for understanding the molecule's potential to exist in different stereoisomeric forms, which are molecules that have the same molecular formula but differ in the three-dimensional orientations of their atoms in space.

Decoding Organic Compound Nomenclature

The nomenclature of organic compounds is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It's paramount for students to understand this system to communicate unambiguously about organic molecules.

Understanding IUPAC Naming

Breaking down '2-bromo-2-chloro-3-methylpentane': 'Pentane' signifies a five-carbon alkane chain. Prefixes 'bromo' and 'chloro' represent bromine and chlorine substituents, while 'methyl' indicates a one-carbon substituent. The numbers specify the carbon atoms' positions these groups are attached to. The sequence in which these substituents are placed in the compound's name often follows the alphabetical order. Mastering IUPAC rules can significantly help students in drawing and identifying diverse organic molecules.

Exploring Structural Isomerism

Structural isomerism is yet another intriguing concept in organic chemistry. It encompasses molecules that have the same molecular formula but differ in how the atoms are connected to each other, leading to varying physical and chemical properties. Structural isomers can be categorized into several types, including chain isomers, where the carbon chain arrangement varies, and position isomers, where the functional groups are located differently along the main carbon chain.

For example, in our textbook problem, if the bromine or chlorine were positioned on different carbon atoms, it would result in a structural isomer of the given compound. Recognizing isomerism is crucial for understanding that molecules with identical formulas can behave very differently. It also highlights the importance of precise nomenclature to distinguish these isomers.