PESSpectrumofMethaneC4H2t213a1LUMO2p1sHOMO2s1t2N/2a12a122.42.21.81.61.41.2lonizationEnergy(eV)MOTheory explainsthe PESquitewell!
C 4H 2p 2s 1s 2a1 3a1 1t2 2t2 1t2 2a1 MO Theory explains the PES quite well!
2t2C4H3a12p1sH2py2px2P1t22s1t2MO model2a12s / 2a1VB modelTheMOmodelofCH.doesnotsigma bondsLexplicitlyreflect the4equivalent Cbetweensand sp3orbitalsHo-bonds of"chemical intuitionastheVBmodeldoes!UVB=HO,(1)·Φ(2)+HO(2)·Φ(1)CHHowcantheMOmodel becomechemicallyintuitiveastheVBmodel does ?http://www.science.oregonstate.edu/~gablek/CH334/Chapter1/methaneMOs.htm
VB model http://www.science.oregonstate.edu/~gablek/CH334/Chapter1/methane_MOs.htm C 4H 2p 2s 1s 2a1 3a1 1t2 2t2 MO model 2a1 1t2 The MO model of CH4 does not explicitly reflect the 4 equivalent CH -bonds of “chemical intuition” as the VB model does ! How can the MO model become chemically intuitive as the VB model does ? (1) ( 2 ) ( 2 ) (1) CHi i i i i VB HO HO
Now considerthe linear combinations of thefour CMOsY=(,+,+,+)/2Y,=(s + x-V,- W)/2Let Cb= CdY3=(s-Wx- V, + W)/2Y4=(-++ V,- )/2& ca=CcY1 = [(c,C2s+ca(C2p,+C2p,+C2p.)+(ca+3c)Φi+(ca-C)(Φ2+Φ3+Φ4) ]/2Y,=cl(C2s+C2p,+C2p,+C2p.)/2+ca*ΦLocalized molecularY2= Cb(C2s-C2px-C2p,+C2p-)/2 + caΦ2orbitals(LMOs)describing C-H bondsY3= cb(C2s-C2p,+C2p,-C2p.)/2 + caΦ3Y4 = cb(C2s+C2px-C2p,-C2p.)/2 + ca'Φ4中h2dh14 sp3-hybridized orbitals on Cdh3The4LMOsareineffect similartothose4covalent C-H bonds described in VB theory
Now consider the linear combinations of the four CMOs, h1 h2 h4 h3 z x y a b c d 1= (s + x + y + z )/2 2= (s + x – y – z )/2 3= (s – x – y + z )/2 4= (s – x+ y – z )/2 1 = [(cbC2s+cd (C2px+C2py+C2pz )+(ca+3cc )1+(ca -cc )(2+3+4 )]/2 Let cb= cd & ca=cc 1 = cb (C2s+C2px+C2py+C2pz )/2+ca 1 2 = cb (C2s–C2px–C2py+C2pz )/2 + ca 2 3 = cb (C2s–C2px+C2py–C2pz )/2 + ca 3 4 = cb (C2s+C2px–C2py–C2pz )/2 + ca 4 Localized molecular orbitals (LMOs) describing C-H bonds 4 sp3-hybridized orbitals on C The 4LMOs are in effect similar to those 4 covalent C-H bonds described in VB theory
主观题10分设置Are thefour LMOs of CH4 equal in energy?If so,please prove that after class!Q1:Notethat hybrid orbitals areused inboththeVBand LMO descriptions ofa covalent bond (e.g.,in CH4)Whatisthedifference inthetwo models?Q2:Howtoconstructhybridized atomicorbitalsforfurtherconstructionofLMOsofamolecule?正常使用主观题需2.0以上版本雨课堂作答
Are the four LMOs of CH4 equal in energy? If so, please prove that after class! 作答 正常使用主观题需2.0以上版本雨课堂 Q1: Note that hybrid orbitals are used in both the VB and LMO descriptions of a covalent bond (e.g., in CH4 ). What is the difference in the two models? Q2: How to construct hybridized atomic orbitals for further construction of LMOs of a molecule ? 主观题 10分
Content of this chapterHybrid Orbital Theoryg-bonds/o-frameworkofa molecule (Qualitative2.VSEPRModel(after-class)MO&VBtheory)元-bonds of a molecule3.Delocalized元-coniugationVB&MOtheories.and Delocalized MO TheoryQualitative)4.Hickel MO Theory and(Semi-QuantitativelSemiempiricalMO)Coniugated Systems5.Symmetry Rules forMolecularreactions(Qualitative)Molecular Reactions
4. Hückel MO Theory and Conjugated Systems Content of this chapter 1. Hybrid Orbital Theory -bonds/-framework of a molecule (Qualitative, MO&VB theory ) 5. Symmetry Rules for Molecular Reactions -bonds of a molecule (VB & MO theories, Qualitative ) (Semi-Quantitative/ Semiempirical MO) Molecular reactions (Qualitative) 3. Delocalized -conjugation and Delocalized MO Theory 2. VSEPR Model (after-class)