OrbitalsUniversityofNorthCarolinaWilmington轨道课件.ppt

1、CHM211(OrganicChemistry)Summer2010nDr.Ned H.Martin nOffice:Dobo 242EnTelephone:n 962-3453(campus)nEmail:martinnuncw.edu1第1页，共40页。TextsnOrganic Chemistry,7th edition,McMurrynOptionalnStudy Guide and Solutions Manual for McMurrys Organic Chemistry,7th editionnMolecular model kitnCourse Website(Syllabu

2、s,Grading Policy):http:/www.uncw.edu/chem/Courses/Martinn/chm211martin/index.htm2第2页，共40页。GradingPolicynFour 40-minute tests,each worth 60 points.nThe final exam will consist of six sections.The first four are like the four tests;the higher grade counts.Section 5 is new material(since the last test)

3、.Section 6 is comprehensive.You may take(or not)as many of the first four sections as you want.Everyone must take sections 5 and 6.nThere will be no make up exams.nEach of the tests may include at least one problem from the homework assignments.Tests 2-4 may contain one review question from the prev

4、ious test.n93%=A,90%=A-,87%=B+,84%=B,80%=B-,etc.3第3页，共40页。Attendance&HomeworknAttendance is expected,but not officially monitored for grading purposes.nMissing 1 day in the summer is like missing 1 week during a regular semester!nHomework problems are assigned,but not collected.nActively working the

5、 homework problems allows you to test whether you understand the material and serves as a review guide for the exams.4第4页，共40页。KeystoSuccessinCHM211nMemorization alone is not sufficient.nReasoning alone is not sufficient.nStudy three times:n Before the lecturen After the lecturen Before the testnAct

6、ively do problems(Keep a notebook).nCooperate form study groups.5第5页，共40页。WhatisOrganicChemistry?nThe study of carbon-containing compoundsnImportant because:nCarbon forms 4 bonds,and can bond to itself in long chainsnCarbon has three different geometries giving rise to a variety of structuresnCarbon

7、 bonds strongly to other common elements:O,N,Cl,etc.nOrganic compounds have many applications and uses:dyes,medicines,fabric,plastics,food(protein,carbohydrates,fats,oils),fuel,pesticides,paint,preservatives,hormones,etc.nThis PowerPoint covers:Chapter 1.Structure and Bonding6第6页，共40页。C(Carbon)nCarb

8、ons atomic number=6,therefore it has 6 protons in its nucleus.nA neutral atom of 12C has 6 protons,6 neutrons and 6 electrons;its amu=12 (=6p+6n)nA neutral atom of 13C has 6 protons,7 neutrons and 6 electrons;its amu=13 (=6p+7n)nA neutral atom of 14C has?protons,?neutrons and?electrons;its amu=?(=?p

9、+?n)nCarbons atomic weight=12.011;this is a weighted average of the three isotopes:12C,13C,and 14C.7第7页，共40页。PartsofanAtomnProtons(+charge)and neutrons(0 charge)are in the center or nucleus of the atomnElectrons(-charge)are considered to be a cloud of charge around the nucleus.Orbitals describe wher

10、e the electrons are.Electrons have very little mass compared to protons and neutrons.nElectrons are found in s orbitals(spherical),p orbitals(dumbbell),or d orbitals(various shapes)nElectrons are grouped in different layers or shells.8第8页，共40页。1.1AtomicStructurenStructure of an atomnPositively charg

11、ed nucleus(very dense,protons and neutrons)and small(10-15 m)nNegatively charged electrons are in a cloud(10-10 m)around nucleusnDiameter is about 2 10-10 m(200 picometers(pm)the unit Angstrom()is 10-10 m=100 pm9第9页，共40页。1.2AtomicStructure:OrbitalsnQuantum mechanics:describes electron energies and l

12、ocations by a wave function,nA plot of 2 describes the region where electrons are most likely to benAn electron cloud has no specific boundary so we represent its shape by the region of highest probability of finding an electron.nSolutions of the wave equation give rise to regions of electron densit

13、y on each atom of specific shapes(atomic orbitals)10第10页，共40页。ShapesofAtomicOrbitalsnFour different kinds of orbitals occupied by electronsnDenoted s,p,d,and f(listed in increasing energy)ns and p orbitals are most important in organic chemistryns orbitals:spherical,with the nucleus at centernp orbi

14、tals:dumbbell-shaped,with the nucleus at the center11第11页，共40页。p-OrbitalsnThere are three perpendicular p orbitals,px,py,and pz,of equal energynLobes of a p orbital are separated by region of zero electron density,called a node.12第12页，共40页。1.3AtomicStructure:e-ConfigurationnThe lowest energy electro

15、n configuration of an atom of any element can be predicted by following three rules:nThe aufbau principle:Electrons are filled into the lowest energy orbitals first(1s,then 2s,then 2p,then 3s,then 3p,then 4s,then 3d)nThe Pauli exclusion principle:Only two electrons may occupy an orbital;they must ha

16、ve opposite spin orientations.nHunds rule:If there are two or more equal energy(degenerate)orbitals available,the electrons will spread out among the orbitals with parallel spins,only pairing up after the orbitals are half-filled.13第13页，共40页。ExamplesofElectronConfiguration1s2s2px2py2pzHCNOFat.#16789

17、3s3px3py3pzNe10Cl1714第14页，共40页。1.4TheNatureoftheChemicalBondnAtoms form bonds because the compound that results is more stable than the separate atoms.nIonic bonds in salts form as a result of electron transfers,followed by electrostatic attraction between opposite charges.nOrganic compounds form co

18、valent bonds by sharing electrons(G.N.Lewis,1916).nLewis structures show valence electrons of an atom as dots.nHydrogen has one dot,representing its 1s electron.nCarbon has four dots(2s2 2p2).nStable molecule results in a completed shell,an octet(eight e-)for main-group atoms(two for hydrogen).15第15

19、页，共40页。NumberofCovalentBondstoanAtomnAtoms with one,two,or three valence electrons form one,two,or three bonds.nAtoms with four or more valence electrons form as many bonds as they need electrons to fill the s and p levels of their valence shells to reach a stable octet.nCarbon has four valence elec

20、trons(2s2 2p2),therefore forms four bonds(CH4).16第16页，共40页。ValenceofOxygenandNitrogennOxygen has six valence electrons(2s2 2p4),so it forms two bonds(H2O).17第17页，共40页。ValenceofNitrogennNitrogen has five valence electrons(2s2 2p3),and it forms three bonds(NH3).18第18页，共40页。Non-bondingelectronsnValence

21、 electrons not used in bonding are called nonbonding electrons,or lone-pair electrons.nConsider the nitrogen atom in ammonia(NH3):nN shares six valence electrons in three covalent bonds;the remaining two valence electrons are a nonbonding(lone)pair.19第19页，共40页。1.5ValenceBondTheorynCovalent bond form

22、s when two atoms approach each other closely so that a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom.nElectrons are paired in the overlapping orbitals and are attracted to nuclei of both atoms.nThe HH bond results from the overlap of two singly occupied hyd

23、rogen 1s orbitals.nThe H-H bond is cylindrically symmetrical,sigma(s s)bond.20第20页，共40页。BondEnergynThe reaction 2 H H2 releases 436 kJ/mol.nThe product has 436 kJ/mol less energy than two H atoms:HH has bond strength of 436 kJ/mol.(1 kJ=0.2390 kcal;1 kcal=4.184 kJ).21第21页，共40页。BondLengthnDistance be

24、tween nuclei that leads to maximum stability.nIf too close,they repel because both nuclei are positively charged.nIf nuclei are too far apart,bonding is weak.22第22页，共40页。1.6Hybridization:sp3 OrbitalsandtheStructureofMethanenCarbon has 4 valence electrons(2s2 2p2)nIn CH4,all CH bonds are identical(te

25、trahedral)nHow can this be explained?23第23页，共40页。1.6Hybridization:sp3 OrbitalsandtheStructureofMethanensp3 hybrid orbitals:s orbital and three p orbitals combine to form four equivalent,unsymmetrical,tetrahedral orbitals(s+p+p+p=sp3),Pauling(1931)24第24页，共40页。TetrahedralStructureofMethanensp3 orbital

26、s on C overlap with 1s orbitals on 4 H atoms to form four identical C-H bondsnEach CH bond has a strength of 438 kJ/mol and length of 110 pmnBond angle:each HCH is 109.5,the tetrahedral angle.25第25页，共40页。1.7Hybridization:sp3 OrbitalsandtheStructureofEthanenTwo Cs bond to each other by s overlap of a

27、n sp3 orbital from each C.nThe other three sp3 orbitals on each C overlap with H 1s orbitals to form six CH bonds.nThe CH bond strength in ethane is 420 kJ/mol.nThe CC bond is 154 pm long and its strength is 376 kJ/mol.nAll bond angles of ethane are tetrahedral.CCHHHHHH26第26页，共40页。1.8Hybridization:s

28、p2 OrbitalsandtheStructureofEthene(Ethylene)nsp2 hybrid orbitals:A 2s orbital of C combines with two 2p orbitals,giving 3 orbitals(s+p+p=sp2)nsp2 orbitals are in a plane with 120 angles nRemaining p orbital is perpendicular to the plane90120CCHHHH27第27页，共40页。Carbon-CarbonBondsinEthenenTwo sp2-hybrid

29、ized orbitals overlap to form a s bondnTwo p orbitals overlap side-to-side to form a pi()bondnsp2sp2 s bond and 2p2p bond results in sharing four electrons and formation of C=C double bondnElectrons in the s bond are centered between nucleinElectrons in the bond occupy regions on either side of a li

30、ne between nuclei,above and below the plane of the atoms.28第28页，共40页。Carbon-HydrogenBondsinEthenenEach of 4 H atoms form s bonds with four sp2 orbitalsnHCH and HCC bond angles are about 120 nC=C double bond in ethene is shorter and stronger than the C-C single bond in ethane nThe ethene C=C bond len

31、gth is 133 pm(Recall that the CC bond length in ethane is 154 pm)nThe C+C bond strength is 611 kJ/mol,less than twice the strength of a C-C(2 x 376=752).29第29页，共40页。1.9Hybridization:sp OrbitalsandtheStructureofAcetylenenThe in acetylene(ethyne)is a triple bond,with the carbons sharing six electronsn

32、A carbon 2s orbital hybridizes with a single p orbital giving two sp hybridsnThe other two p orbitals on each C remain unchangednsp orbitals are linear,oriented 180 apart(on x-axis)nThe two p orbitals are perpendicular,on the y-axis and the z-axisCCHHCC30第30页，共40页。OrbitalsofAcetylenenTwo sp hybrid o

33、rbitals from each C overlap to form an spsp s bond.nTwo pz orbitals from each C form a pzpz bond by sideways overlap;py orbitals overlap similarly to form a second bond.31第31页，共40页。BondinginAcetylenenSharing of six electrons forms a .nTwo sp orbitals form s bonds with hydrogens.nThe bond strength is

34、 835 kJ/mol,much less than three times the strength of a C-C(3 x 376=1128).The bond length is 120 pm.CCCCCC32第32页，共40页。1.10HybridizationofOtherElementsnElements other than C can have hybridized orbitals.nThe HNH bond angle in ammonia(NH3)is 107.3,close to the tetrahedral 109.5.nNs orbitals(s+p+p+p)h

35、ybridize to form four sp3 orbitals.nOne sp3 orbital holds two nonbonding electrons,and three sp3 orbitals have one electron each,forming s bonds to three Hs.33第33页，共40页。HybridizationofOxygeninWaternThe oxygen atom is sp3-hybridized.nOxygen has six valence-shell electrons but forms only two covalent

36、bonds,leaving two lone pairs.nThe HOH bond angle is 104.5,slightly smaller than the perfect tetrahedral angle(109.5)because of electron-electron repulsion between the lone pairs.34第34页，共40页。1.11MolecularOrbitalTheorynA molecular orbital(MO):where electrons are most likely to be found(specific energy

37、 and general shape)in a molecule.nThe two(or more)atomic orbitals combine to make two(or more)molecular orbitals.nAdditive combination(bonding)MO is lower in energy.nSubtractive combination(antibonding)MO is higher.35第35页，共40页。MolecularOrbitalsinEthenenThe bonding MO results from combining p orbital

38、 lobes with the same algebraic sign.nThe antibonding MO comes from combining lobes with opposite signs.nOnly the bonding MO is occupied by electrons.36第36页，共40页。SummarynOrganic chemistry chemistry of carbon compoundsnAtom:positively charged nucleus surrounded by negatively charged electronsnElectron

39、s occupy orbitals around the nucleus.nDifferent orbitals have different energy levels and different shapesns orbitals are spherical,p orbitals are dumbbell-shapednCovalent bonds-electron pair is shared between atomsnValence bond theory-electron sharing occurs by overlap of two atomic orbitals37第37页，

40、共40页。Summary,contdnHybrid Atomic Orbital Theory-electron sharing occurs by overlap of two orbitals formed by combining(hybridizing)two or more atomic orbitals(sp,sp2,sp3)nMolecular orbital(MO)theory-bonds result from combination of atomic orbitals to give molecular orbitals,which belong to the entir

41、e moleculenSigma(s s)bonds-Circular in cross-section and are formed by head-on interactionnPi()bonds “dumbbell”shape,from sideways interaction of p orbitals;located above and below the s bond framework of the molecule38第38页，共40页。Summary,contd.nCarbon uses hybrid orbitals to form bonds in organic mol

42、ecules.nIn single bonds with tetrahedral geometry,carbon has four sp3 hybrid orbitalsnIn double bonds with planar geometry,carbon uses three equivalent sp2 hybrid orbitals and one unhybridized p orbitalnCarbon uses two equivalent sp hybrid orbitals to form a triple bond with linear geometry,with two

43、 unhybridized p orbitalsnAtoms such as nitrogen and oxygen also hybridize to form strong,oriented bondsnThe nitrogen atom in ammonia and the oxygen atom in water are sp3-hybridized 39第39页，共40页。QuickReviewnCarbonnOne s and three p orbitals hybridize to form four sp3 orbitalsnIn methane and ethane,C is tetrahedral,with 109.5 bond anglesnIn ethene,One s and two p orbitals hybridize to form three sp2 orbitals.The bonds between the nuclei are the s bonds from the overlapped sp2 orbitals.The remaining p orbitals overlap side-to-side to form a bond.C-C bonds are weaker than C-C s bonds.40第40页，共40页。