Give the name or condensed structural formula, appropriate: (a) CCCCC(C)CC(C)C (b) 2,2 -dimethylpentane (c) 4 -ethyl-1,1-dimethylcyclohexane (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}\) (e) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

SMILES (Simplified Molecular Input Line Entry System) notation plays a crucial role in representing chemical structures in a linear text form. This compact and easy-to-use method allows chemists to depict complex molecules using simple ASCII strings, facilitating digital communication and database searching for chemicals.

For example, the SMILES string CCCCC(C)CC(C)C corresponds to a chemical structure which is more comprehensively represented by its condensed structural formula, as shown in the exercise above. To understand SMILES, you need to grasp that carbon chains are shown by a sequence of 'C' characters, branches are denoted by parentheses, and bonds between atoms are often implicit, assumed to be single unless otherwise specified.

Systematic chemical nomenclature is a methodical way of naming chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It ensures that each chemical compound has a unique and universally accepted name.

Here's an example: the name '2,2-dimethylpentane' may look just like a string of words, but it precisely describes the molecule's structure using IUPAC conventions. The 'pentane' part tells us that there is a five-carbon hydrocarbon chain, and '2,2-dimethyl' indicates that there are two methyl groups (-CH₃) attached to the second carbon of the chain.

Breaking Down Systematic Names

• Root Name: Indicates the number of carbon atoms in the longest chain (e.g., 'pent' for five carbons).
• Prefix: Describes the nature and position of substituents (e.g., 'methyl' for -CH₃).
• Locant: Numerical prefixes (e.g., '2,2-') tell the positions of these substituents on the main chain.

Through the systematic nomenclature, students can derive a clear structural formula of a compound from its name.

The condensed structural formula is a more compact representation of a molecule's structure compared to its full Lewis or Kekulé structures. They provide a balanced middle ground between the full structural detail and the brevity of chemical formulas.

For example, the structural formula for 4-ethyl-1,1-dimethylcyclohexane can be represented as \[\left[\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{CH}\left(\mathrm{C}_{2}\mathrm{H}_{5}\right)\mathrm{CH}_{2}\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}\right]_{6}\] emphasizing how the substituents like ethyl (C₂H₅) and methyl (CH₃) groups are arranged around the cyclohexane ring.

Advantages of Using Condensed Formulas

• They save space and time without losing essential structural information.
• They help avoid the complexity while still indicating the connections between atoms.
• Suitable for quick comparative analyses of similar compounds.

Condensed formulas greatly aid in understanding and analyzing organic molecules without the laboriousness of drawing out full structural diagrams.