University:
Kentucky State University
Course:
CHE 302 | Organic Chemistry II
Academic year:

2021
Views:

354

Pages:

11
Author:

strofamay58

Lecture 2 - Alcohol **Physical Properties** * **Dipole-dipole interaction:** H-O-H δ+ δ- δ+ * (δ-) partial negative with (δ+) partial positive * Dipole-dipole = attraction between +ve end and the -ve end of another. * **Electronegativity:** Li Be B C N O F Ne * increases * most electronegative atom (F) * e.g., C-N * These electrons will spend most of their time near N C-O-H δ+ δ- δ+ * Dipole-dipole interaction * Dipole: Di-pole * a compound has 2 or more partial charges C-O-C δ- δ+ δ- * Dipole-dipole interaction between H and (O, N, F) → is Hydrogen bond C-O-H ... H - hydrogen bond H-O-R * dipole-dipole interaction is relatively weak, but Hydrogen bond is stronger (relatively) because of H is very strong because it has only 1 electron and this electron is attached to highly electronegative atom. → alcohols are polar molecules because they make a Hydrogen bonding. → in brief: it makes molecules more polar - it makes them more water-soluble - increases their boiling point (because they have stronger interaction that typical dipole-dipole so they have a significant effect on their physical properties) → Hydrogen bond ARE NOT covalent bonds. Covalent bond is much stronger. Importance of Hydrogen bonding * Ethanol & dimethyl ether are Constitutional isomers ** * Compounds have the same chemical formula but they differ in how atoms are bonded. C₂H₆O CH₃CH₂OH Ethanol CH₃OCH₃ dimethyl ether B.P: 78°C -24°C * Oxygen is bonded to H * Oxygen is not bonded to H so this compound can can't make H-B make hydrogen bond only dipole-dipole interaction * Existence of -OH groups: * makes molecules more soluble in water * higher boiling point * presence of additional -OH group increases solubility in water & boiling point