columbia大学有机化学课件01_15_19 html

1、1.15Bonding in Methane and Orbital Hybridizationtetrahedralbond angles = 109.5 bond distances = 110 pmbut structure seems inconsistent withelectron configuration of carbonStructure of Methane only two unpaired electronsshould form s bonds to only two hydrogen atomsbonds should be at right angles to

2、one another2p2sElectron configuration of carbon2pPromote an electron from the 2sto the 2p orbital2ssp3 Orbital Hybridization2p 2p2s2ssp3 Orbital Hybridization2p Mix together (hybridize) the 2s orbital and the three 2p orbitals2ssp3 Orbital Hybridization2p 2 sp3 4 equivalent half-filled orbitals are

3、consistent with four bonds and tetrahedral geometry2ssp3 Orbital HybridizationpsShapes of orbitalsp+sNodal properties of orbitalsp+take the s orbital and place it on top of the p orbital+sShape of sp3 hybrid orbitalss + p+reinforcement of electron wave in regions where sign is the samedestructive in

4、terference in regions of opposite signShape of sp3 hybrid orbitalssp hybrid+orbital shown is sp hybridanalogous procedure using three s orbitals and one p orbital gives sp3 hybridshape of sp3 hybrid is similarShape of sp3 hybrid orbitalssp hybrid+hybrid orbital is not symmetricalhigher probability o

5、f findingan electron onone side of the nucleus than the otherleads to stronger bondsShape of sp3 hybrid orbitalsIn-phase overlap of a half-filled 1s orbital ofhydrogen with a half-filled sp3carbon:hybrid orbital of+ Hssp3+C gives a s bond.+HC sC HThe CH s Bond in Methaneconsistent with structure of

6、methaneallows for formation of 4 bonds rather than 2bonds involving sp3 hybrid orbitals are stronger than those involving s-s overlap or p-p overlapJustification for Orbital Hybridization1.16sp3 Hybridization and Bonding in EthaneC2H6CH3CH3tetrahedral geometry at each carbonCH bond distance = 110 pm

7、 CC bond distance = 153 pmStructure of EthaneIn-phase overlap of half-filled sp3orbital of one carbon with half-filled sp3hybrid orbital of another.Overlap is along internuclear axis to give a sbond.hybridThe CC s Bond in EthaneIn-phase overlap of half-filledorbital of one carbon with half-filled sp

8、3hybrid orbital of another.Overlap is along internuclear axis to give a sbond.sp3 hybridThe CC s Bond in Ethane1.17sp2 Hybridization and Bonding in EthyleneC2H4H2C=CH2planarbond angles: bond distances:close to 120CH = 110 pmC=C= 134 pmStructure of Ethylene2pPromote an electron from the 2sto the 2p o

9、rbital2ssp2 Orbital Hybridization2p 2p2s2ssp2 Orbital Hybridization2p Mix together (hybridize) the 2s orbital and two of the three 2p orbitals2ssp2 Orbital Hybridization2p 2 sp2 3 equivalent half-filled sp2 hybrid orbitals plus 1 p orbital left unhybridized2ssp2 Orbital Hybridizationp2 of the 3 sp2

10、orbitalsare involved in s bonds2 sp2 to hydrogens;the otheris involved in a s bondto carbonsp2 Orbital Hybridizationp2 sp2 ssosssp2 Orbital Hybridizationthe unhybridized p orbital of carbon is involved in p bondingto the other carbonp2 sp2 p Bonding in Ethylenep Bonding in Ethylenep Bonding in Ethyl

11、ene1.18sp Hybridizationand Bonding in AcetyleneC2H2HCCHlinearbond angles: bond distances:180CH = 106 pmCC= 120 pmStructure of Acetylene2pPromote an electron from the 2sto the 2p orbital2ssp Orbital Hybridization2p 2p2s2ssp Orbital Hybridization2p Mix together (hybridize) the 2s orbital and one of th

12、e three 2p orbitals2ssp Orbital Hybridization2p 2 p2 sp2 equivalent half-filled sp hybrid orbitals plus 2 p orbitals left unhybridized2ssp Orbital Hybridization2 p1 of the 2 sp orbitalsis involved in a s bond2 spto hydrogen;the otheris involved in a s bondto carbonsp Orbital Hybridization2 p2 spssss

13、p Orbital Hybridizationthe unhybridized p orbitals of carbon are involved in separatep bonds to the other carbon2 p2 spp Bonding in Acetylenep Bonding in Acetylenep Bonding in Acetylenep Bonding in Acetylene1.19Which Theory of Chemical Bonding is Best?Lewismost familiareasiest to apply Valence-Bond (Orbital Hybridization)provides more insight than Lewis modelability to