Organic Chemistry: Isomerism

• General organic chemistry involves studying carbon-containing compound structures, properties, composition, reactions, and preparation. This includes hydrocarbons and compounds featuring elements like hydrogen, nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur.
• The focus is on understanding the relationship between molecular structure and chemical reactivity to predict and explain how organic molecules participate in chemical reactions

Isomerism

• Isomers are molecules sharing a molecular formula but differing in structural formulas or atomic spatial arrangement.
• Isomerism is a phenomenon where multiple compounds share a chemical formula but possess different chemical structures.

Structural Isomers

• Also known as constitutional isomers, they share a molecular formula but differ in atomic connectivity.
• Chain isomers exhibit differences in the arrangement of the carbon skeleton.
• Position isomers vary in the positioning of a substituent group on the same carbon skeleton.
• Functional group isomers share a molecular formula but differ in functional groups.

Stereoisomers

• Stereoisomers possess the same molecular formula and atomic connectivity but differ in the spatial arrangement of atoms.

Geometric Isomers

• Also known as cis-trans isomers, they arise from restricted bond rotation, typically around a double bond or within cyclic compounds.
• Cis isomers feature substituents on the same side of the double bond or ring.
• Trans isomers feature substituents on opposite sides of the double bond or ring.

Optical Isomers

• Stereoisomers that are non-superimposable mirror images of each other.
• Enantiomers is another term for optical isomers.
• A chiral center (or stereocenter) is an atom, typically carbon, bonded to four different groups.
• Molecules housing chiral centers demonstrate optical activity, enabling them to rotate plane-polarized light.
• Enantiomers induce opposite rotations of plane-polarized light.
• A racemic mixture, containing equal enantiomer amounts, lacks optical activity.
• Diastereomers are stereoisomers that are not mirror images.

Resonance

• Resonance describes electron delocalization in molecules/ions where bonding is not expressible via a single Lewis structure.
• Resonance structures represent different possible Lewis structure drawings for the same molecule.
• The actual molecular structure is a hybrid of all resonance structures, known as the resonance hybrid.
• Resonance structures are linked by a double-headed arrow.
• Resonance structures differ solely in electron distribution, not in atomic arrangement.
• Resonance structures contribute differently to the resonance hybrid; more stable structures contribute more.
• Stability is enhanced by minimizing formal charges, maximizing atoms with complete octets, and placing negative charges on more electronegative atoms.
• Electron delocalization via resonance generally stabilizes a molecule.

Hyperconjugation

• Hyperconjugation involves the interaction of sigma (σ) bonding electrons (usually C-H or C-C bonds) with an adjacent empty or partially filled p-orbital or a π-orbital.
• This interaction is stabilizing, leading to electron density delocalization.
• No bond resonance is another term for hyperconjugation.
• Hyperconjugation explains the stability of more substituted alkenes.
• An increased number of alkyl groups attached to doubly bonded carbon atoms leads to greater hyperconjugation and greater alkene stability.
• Hyperconjugation impacts the stability of carbocations.
• More substituted carbocations exhibit greater stability due to the hyperconjugative effect of adjacent alkyl groups.

Functional Groups

• Functional groups are specific atomic groups within molecules responsible for the molecule's characteristic chemical reactions.
• Alkanes exclusively contain single bonds between carbon and hydrogen atoms (C-H) and carbon atoms (C-C).
• Alkenes feature at least one carbon-carbon double bond (C=C).
• Alkynes feature at least one carbon-carbon triple bond (C≡C).
• Alcohols contain a hydroxyl group (-OH) bonded to a carbon atom.
• Ethers feature an oxygen atom bonded to two alkyl or aryl groups (R-O-R').
• Aldehydes contain a carbonyl group (C=O) with at least one hydrogen atom attached to the carbonyl carbon.
• Ketones contain a carbonyl group (C=O) with two alkyl or aryl groups attached to the carbonyl carbon.
• Carboxylic acids contain a carboxyl group (-COOH).
• Esters contain a carbonyl group (C=O) with an oxygen atom bonded to the carbonyl carbon and another alkyl or aryl group (R-COO-R').
• Amines feature a nitrogen atom with one, two, or three alkyl or aryl groups attached (R-NH2, R2NH, R3N).
• Amides contain a carbonyl group (C=O) bonded to a nitrogen atom (R-CO-NH2, R-CO-NHR', R-CO-NR'R'').
• Nitriles contain a cyano group (-C≡N).
• Halides contain a halogen atom (F, Cl, Br, I) bonded to a carbon atom.
• Aromatic compounds contain a benzene ring or similar system with delocalized π electrons.