Bài giảng Organic Chemistry - 1. Organic Chemistry: The Chemistry Of Carbon

RachmaninovOrganic Chemistry:The Chemistry Of CarbonChemistry 3The (a) view of your existence.hellI,too,started small..Peter VollhardtUniversity of California at BerkeleyThe Fun of Organic ChemistryTigre Delta, Buenos Aires, 1952Organic ChemicalsMore ChemicalsMmmmmmmmmmmmmhhhh!!!!Public Fear Of ChemistryThe Obsession With “Natural”Hello ???! Nature Is ViciousChemical Protection In NatureSolanineNausea, diarrhea, vomiting, cardiac dysrhythmia, hallucinations, paralysis, hypothermia, and deathChemical Warfare In NatureThe Bombardier BeetleBenzoquinone,hydrogen peroxide, 100ºCMP4The Californian Sea Hare Defends Itself From Predators With Sticky InkAplysia californica Nature Is The Biggest PolluterThiols (And Sulfides) Stink.Decomposing food, passing gas, power plants, natural gas additive methanethiol, stink bombs, waste water,feces, some chemistry departments..Skunk chemical defense:Body odour:But May Be Very Pleasant InLow ConcentrationsGrapefruitCan be tasted at the 10-5 ppb level!!1 mg in 10 million liters Roasted coffee Black teaSex pheromone of the spruce budworm, the most destructive pest to the spruce and fir forests of North AmericaPheromones: Chemical Communication(E)-11-tetradecenalThe Holy Grail: Human Sex PheromonesC&EN, Feb. 2003SteroidsPolymersLatex: precursorto natural rubberPolyacetylene: Organic ConductorsHeeger, MacDiarmid, Shirakawa, Nobel prize 2000The polyamide KevlarBulletproof!Organic Polymers Harder Than MetalMedicinesTop 5 Drugs Worldwide (by Sales)Cholesterol reducerBlood clotsArthritisAntiasthmaticAntirheumaticAspirin: the Most Successful Drug of All TimesAnalgesic, antipyretic, anti-inflammatory, antiplateletBlood clotWhat to Expect: An OutlineSyllabusAtom 1 + Atom 2 A:A (A A) or A+A− “favorable” “Rules”: 1. Opposite charges attract each other (Coulomb) 2. Electrons spread out in space (delocalization) Chapter 1:BondingA Review Of Chem 1Charles Augustin de Coulomb1736-1806Classical view of atom (Bohr)Bond Strength And LengthBond strengthCovalent Bonding: Sharing ElectronsDimensions:Nuclear diameter ~ 10-15 mElectronic orbit ~ 10-10 mfive orders of magnitudeMass ratio proton : electron = ~ 1800Ionic Bonding: “No” Sharing of Electrons Who donates and who accepts?Valence electronsDuetOctetsPartial Periodic TableWhy Do Elements React?Aim“Ionic” BondsLi2,1Na2,8,1F2,7[Li2]+[Na2,8]+[F2,8]-+1e-1e-1eTherefore:+-Noble Gas Configuration2 Na FF22 Na+BooomTransfer of Valence Electrons-4eShows onlyvalence e (He)(Ne)Compromise: electron-sharingC..HHHH......H O H........2. “Covalent” BondsC4++4e4 HCC2 H2O2++BooomC4-Elements in the “middle” of the periodic table have a problem with electron affinity (EA) and ionization potential (IP):Lakehurst, NJ, May 3, 1937The HindenburgMP43. Most Bonds Are “Between” Covalent and Ionic:Polar CovalentHIClH3CF::::-+::::-+-+F::::A:B-+Linus Pauling 1901-1994Examples:dipoleThe Shape Of MoleculesIs Controlled By Valence Electron RepulsionDiatomics: linear (of course), e.g. Triatomics: either linear, e.g. H:HLi:HF::::F::::BeF:::::F:::Beor bent, when there are lone e-pairs, e.g. Tetraatomics: either trigonal, e.g. O::::HHCl::::Cl::::Cl::::BnotF::::F:::or pyramidal, when there are lone e-pairs, e.g.N:HHHPentaatomics: tetrahedral, e.g.HHHHCLewis Structures Draw molecular skeleton (usually given)Rule 1:Count total number of valence electronsRule 2:Octet (Duet) RuleProvide octets (duets for H) around all atomsRule 3:How To Distribute Valence Electrons:CO2O C OCH4CHHHHC......O:..HBr:::..H:HF::::F:::O::::HHGilbert N. Lewis (1875–1946)Take care of charges, if any. Charges occur when the formal “effective” electron count around the nucleus differs from its valence electron count.“Effective” electron count: Each bond with twoshared electrons counts as 1e; lone pairs count as 2e.H3ONOCORule 4::N:::O:+:C:::O:+-H:O:HH....+Valence electron count: Rule 2 (# of valence electrons).++-+Example:1. Atom arrangement:2. Valence electrons:3. Octet ruleShortcut:1. Connect all bonded atoms with “2e line”. 2. If there are e left, add them as lone pairs to any atom to give it an octet until no e left. 3. If some atoms lack octet, move lone pairs into shared positions.CO2:......:..OCOOCO........OCO:......:..OCOO C OO 6e, C 4e16e totalResonanceOften several octet structures are possible for a molecule: Resonance formsForm A form Bmove electrons(pairs)Molecule is a superposition of these formsCarbonate, CO32-. All forms are equivalent..OOCO--..........OCO-............OCO-............-:O:..-:O:..The carbonate ion is delocalized:symmetrical! Electrostatic Potential Map: Red = relatively electron rich Blue = relatively electron poorResonance FormsOCO-..........-:O:..Rules1. Octet rule (wins over all other)Nonequivalent Resonance Forms6e-majorOOHCCHHH+6emajorNNO++which ones are better?O2. When there are two or more forms with complete octets: electronegativity rules.Example: enolate ion charge on more e-negative elementmajorH--HHHHHCCCCOOBut:6emajorNNO++OWhen in doubt, rule 1 wins !3. Minimum charge separationFormic acidmajor-HCCHHHOO+OONote: Rule 1 wins !:C:::O:+-Exceptions To The Octet RuleRadicalsDeficiency of electronsElements beyond the second row (“valence shell expansion”) But we can still write polar octet structureQuantum MechanicsLight And Objects As Waves Or ParticlesClassical viewQuantum mechanical view1900 Planck, Einstein: Light = photons E = hνν = c/λ c (speed of light) = 300,000 km sec-1 h = Planck’s constant = 1.34 x 10-34 cal secAtoms absorb/emit energy in discrete packages: quanta1923 DeBroglie: All mass (m) moving with velocity v has a wavelength λ = h/mv 1927 Heisenberg: Uncertainty (∆) principle ∆ (position) x ∆ (momentum) > h/4 1927 Schrửdinger: Wave equations for an electron moving around the nucleus. Solutions to wave equations are depicted as three-dimensional spheres: Orbitals.Square of a value of the wave equation around the atom = probability of finding the electron there. Spherical (three-dimensional) shape Contrast to mechanical waves (guitar string, rubber band)OrbitalsTwo-dimensional wave+/- = signs, not chargesNodeAmplitude+-0 “ball”spherical “eight”Actual solutions: 1s, 2s, 2px, 2py, 2pz, 3s, 3px, 3py, 3pz, etc. (increasing energy)+-nodeMost Important Orbitals (For Us):#s are related toclassical shellss Orbitalp OrbitalCorrelates with elements in rows of periodic tableThe S Orbitals1s2s1sThe Three 2P OrbitalsThen 3s, 3px, 3py, 3pz, and new solutions to the wavefunctions: five d orbitals2pEnergy diagram depicting solutions as energy “levels”:There are rules for “filling up” levels with e Lower energy orbitals filled first (closed shell) Pauli: Exclusion principle: 2e max in each level Hund’s rule: Equal energy orbitals (i.e. px,y,z) filled with one e each firstelectrons (He)1s2s pxpypzAufbau PrincipleOr: Where The Electrons GoApproximate Energies Of OrbitalsTherefore, description of electronic configurations:H(1s)1; He(1s)2; Li(1s)2(2s)1; Be(1s)2(2s)2; B(1s)2(2s)2(2p)1; C(1s)2(2s)2(2p)2Fill Them UpOverlap of 2 atomic orbitals gives 2 molecular orbitals In phase overlap  bonding molecular orbital (lower E) Out of phase overlap  antibonding molecular orbital (higher E)Bondingantibonding(node)bondingEnergy diagrams1s1s1s2pE-Orbitals “split” energy levels when entering into overlap.-The better the overlap [e.g. same type of orbital, same energy (shell)], the larger the splitting. -For orbitals of unequal energy, the higher orbital “goes up”, the lower “down”.Bonding In H2 And He2The Types Of Orbital OverlapLi:H 2s + 1s. No shape “issues”How does it bond? Use an empty p orbital:Hybridization And GeometryH : Be : H is linear; but Be atom has filled shells (1s)2(2s)2!-++-This allows for bonds by overlap of the H 1s with the Be 2s and 2p orbitals, but gives wrong structure:Better: “Hybridization” of the two orbitals = Intraatomic overlap (“in phase” and “out of phase”) to generate two new hybrid molecular orbitals: s + p  two sp hybrids, with linear arrangement for BeH2SpNote: n atomic orbitals  n new orbitalsWe shall see next that other combinations of intraatomic overlap (hybridization) are possible: s + p + p  3 sp2 with trigonal shapes + p + p + p  4 sp3 with tetrahedral shapeExample: Bonding In BH3. Hybridization To Trigonalsp2Bonding In Methane: Hybridization To Tetrahedralsp3Bonding In Ethane: Overlap Of Two Sp3 Hybrid OrbitalsEthaneMore Sp3 Hybrids: NH3 And H2ODouble And Triple Bonds: A PreviewMolecular Models: Use Them!!!The Dashed-Wedged Line NotationCH4Wrong