University:
Boston University
Course:
CAS CH 641 | Physical Organic Chemistry
Academic year:

2024
Views:

491

Pages:

26
Author:

debatehl4dcq

Hybrid AOs and polyatomic MOs Hybridized AO AO’ss account for central atom shape Central atom AO mixing: Hybrid AO AO’ss Unmixed AO AO’ss have the wrong central atom geometry An s and a p AO make two sp hybrid h b d AO’s ’ 180o angle, angle for SN = 2 Two p’s are unchanged on each atom sp hybrids account for linear geometry 180o angle, angle for SN = 2 Two p’s are unchanged on each atom An s and two p AO’s make three sp2 hybrid AO’s 120o angle, for SN = 3 One p is unchanged on each atom sp2 hybrids account for trigonal planar geometry 120o angle, for SN = 3 One p is unchanged on each atom An s and three p AO’s make four sp3 hybrid AO’s 109o angle, for SN = 4 sp3 hybrids account for tetrahedral geometry Examples CO2, carbon dioxide H2CO, formaldehyde HCO2‐, formate SO2, sulfur dioxide Polyatomic MO recipe 1. Use the Lewis structure to get – the number of electron pairs – make hybrid AO’s on each atom (except H) 2. Sketch the σ framework and place pairs – in each bonding g σ MO – in each nonbonding hybrid AO 3. Sketch the π framework MO’s, MO s, – mark as bonding, nonbonding, antibonding – place remaining pairs (Auf Bau) – get the π bond order σ framework • Hybridization of terminal atoms the same as their central atom • Terminal H never hybridized • One pair in each hybrid AO σ b di MO bonding • One pair in each non‐bonded hybrid AO CO2 sp σ framework sp hybrids overlap to make two sp σ bonding MO’s, leaving two sp nonbonding AO’s. These can hold … CO2 sp σ framework sp hybrids overlap to make two sp σ bonding MO’s, leaving two sp nonbonding AO’s. These can hold … CO2 sp σ framework sp hybrids overlap to make two sp σ bonding MO’s, leaving two sp nonbonding AO’s. These can hold 4 pairs of electrons. CO2 sp σ framework sp hybrids overlap to make two sp σ bonding MO’s, leaving two sp nonbonding AO’s. These can hold 4 pairs of electrons. Th remaining The i i 4 pairs i are in i the th … CO2 π framework π framework • Unused p AO’s AO s form same number of π MO’s • Number of loops and AO overlap determine whether π MO is … – bonding b di (π) ( ) – nonbonding (πn) – antibonding b d (π*) ( *) CO2 π framework 4 pairs are in the (delocalized) π framework 2p pairs in π ((bonding) g) and 2 p pairs in πn ((nonbonding); g); bond order 2 H2CO sp2 σ framework 6 pairs in Lewis structure, 5 pairs in σ framework, and so 1 pair in (localized) π framework. H2CO π framework 1p pair in ((localized)) π framework 1 pair in π (bonding); bond order 1 HCOO‐ sp2 σ framework 9 pairs in Lewis structure, 7 pairs in σ framework, and so 2 pairs in (delocalized) π framework. HCOO‐ π framework 2 pairs i in i (d (delocalized) l li d) π framework f k 1 pair in π (bonding) and 1 pair in πn (nonbonding); bond order 1 SO2 sp2 σ framework 9 pairs in Lewis structure structure, 7 pairs in σ framework, framework and so 2 pairs in (delocalized) π framework. SO2 π framework 2 pairs in (delocalized) π framework 1p pair in π ((bonding) g) and 1 pair p in πn ((nonbonding); g); bond order 1 SO2 correlation diagram Do these on your own HCOOH, formic acid HCOOH H2C=CH‐CH=CH2 NO O3‐, nitrate i For each one, – Write the Lewis structure – Sketch the σ framework and assign its pairs – Sketch the π framework MO’s, identify bonding, nonbonding, antibonding, and assign its pairs, and get the π bond order