CHEM 1810 - Lecture 22 | Lecture Note

University:
University of Virginia
Course:
CHEM 1810 | Introduction to Chemistry
Academic year:

2024
Views:

452

Pages:

2
Author:

Zoe C.

Ozone (O3) Lewis Structure: Shows three oxygen atoms connected by single and double bonds. Needs Formal Charge to make an octet. Localized vs. Delocalized Electrons: Localized: Electrons are confined to specific bonds or lone pairs. Delocalized: Electrons are spread over multiple atoms or bonds, not confined to a single location. 3 p orbitals on 3 atoms = 3 MOs πe- on all 3 O πe- on outer 2 O, node on middle Neither Lewis dot structure is a completely accurate representation. 50-50 in contributing According to MO description: For one bond: 1.5 bonds from since shared btw 2 bonds. Resonance contributors/structures are imaginary models of molecule. Best model is a hybrid of all Sodium Formate (HCOONa) 2 resonance contributors core: 1s² C: sp² + 2p orbital 5σ bonds, 2 π bonds, 2 LP e- density on ends Terminal oxygens most reactive part Nucleophile: Lewis base (e- pair donor) Methyl Formate Structure: A Lewis structure of methyl formate (HCOOCH3) is drawn. Description: Described as an ester, not an aldehyde or ketone. Contains a delocalized functional group. 4 delocalized electrons 3π MO - 3 MO "Since this contributes to hybrid, A is a shorter than normal C-O bond. B is a longer than normal C-O bond." Formamide Structure: A Lewis structure of formamide (HCONH2) is drawn. Description: Amide: atom with lone pair (N) next to π bond (=O) => 1 resonance Core: SN=3, sp² 4 delocalized electrons Separation of charges Contribution: B is shorter and harder to rotate on (partial bond), the N is planar (even if drawn w/ LP, A is longer, and bo of C-O) C-O stretch in amide = 1660 cm⁻¹ C-N = 0.6 "C-O stretch in ester/aldehyde/ketone = 1760 cm⁻¹; second resonance contributor is weighted more, in ester second one has a charge on O (EN atom) => very minor contribution. -c- double bond character ↓ 100 single bond character restricted rotation