organic chem

Organic Chemistry definition

Study of carbon compounds. Carbon forms 4 covalent bonds. C has 4 valence e-.

Tetravalency of Carbon

Carbon always makes 4 bonds (4 single, 2 single+1 double, 1 single+1 triple, 2 double).

Catenation

Ability of C to bond to itself forming chains, branches, rings. C-C-C-C…

Hybridization sp3

1s+3p = 4 sp3 orbitals, tetrahedral 109.5°, sigma only, single bond. Ex: CH4, CH3-CH3. Alkanes, alcohols, amines.

Hybridization sp2

1s+2p = 3 sp2 (120° trigonal planar) + 1 unhybridized p for pi bond. Double bond. Ex: C=C, C=O, C6H6. Alkenes, aldehydes, ketones, benzene.

Hybridization sp

1s+1p = 2 sp (180° linear) + 2 p for 2 pi bonds. Triple bond. Ex: C≡C, C≡N, -C≡CH. Alkynes, nitriles.

Sigma bond (σ)

Head-on overlap of atomic orbitals, strongest, free rotation possible. σ is every single bond. Ex: C-C, C-H.

Pi bond (π)

Sideways overlap of p orbitals, weaker, no rotation, more reactive. C=C = 1σ+1π, C≡C = 1σ+2π.

Electronegativity trend

C 2.5, H 2.1, O 3.5, N 3.0, Cl 3.0. C-H almost non-polar, C-O,N,Cl polar: Cδ+ - Oδ-. Determines polarity.

Homologous series

Series of compounds differing by CH2. Similar chemical properties, gradual physical change. Ex: CH4, C2H6, C3H8.

Degree of Unsaturation (DoU) / IHD

Rings + pi bonds. DoU = C - H/2 + N/2 +1. Halogen counted as H. Ex: C6H6: DoU = 6 - 6/2 +1 = 4 (1 ring +3 pi).

Empirical formula

Simplest whole number ratio of atoms. Ex: CH3COOH -> CH2O.

Molecular formula

Actual number of atoms in molecule. Ex: C2H6, C6H12O6.

Structural formula

Shows connectivity / order of atoms. Ex: CH3-CH2-OH.

Condensed formula

Omits some bonds, uses parentheses. Ex: CH3CH2OH, CH3COCH3, CH3CH(CH3)CH3.

Skeletal / Line-angle formula

C and H omitted, zigzag line. Vertex and end = C. Ex: hexane = zigzag / Most IMAT structures.

Lewis structure

Shows all valence electrons and bonds with dots/lines.

Wedge-dash 3D formula

Wedge = forward (out of plane), dash = backward, solid = in plane. Ex: (R)-lactic acid. Essential for stereochemistry.

C-C single bond

1 sigma, length 154 pm, energy 347 kJ/mol, free rotation, sp3-sp3. Longest and weakest among C-C. Ex: CH3-CH3. Saturated.

C=C double bond

1 sigma +1 pi, length 134 pm, energy 614 kJ/mol, no rotation, planar, sp2-sp2. Ex: CH2=CH2. Unsaturated, addition reactions.

C≡C triple bond

1 sigma +2 pi, length 120 pm, energy 839 kJ/mol, linear, sp-sp, terminal H acidic. Ex: HC≡CH. pKa ~25.

Conjugated system

Alternating single-double: C=C-C=C. p orbitals overlap, delocalized, extra stable. Ex: 1,3-butadiene CH2=CH-CH=CH2.

Isolated vs Cumulated diene

Isolated: C=C-C-C=C separated. Cumulated: C=C=C allene. Stability: Conjugated > Isolated > Cumulated.

Bond angle and shape summary

sp3 109.5° tetrahedral, sp2 120° trigonal planar, sp 180° linear. Bond energy: Triple (839) > Double (614) > Single (347) kJ/mol. Shorter = stronger.

Primary/Secondary/Tertiary/Quaternary Carbon

Classification by number of C attached: 1°=1C, 2°=2C, 3°=3C, 4°=4C. Ex: (CH3)3CH: central C is 3°.

Classification of alcohol carbon

By carbon bearing OH: 1° R-CH2-OH, 2° R2CH-OH, 3° R3C-OH. Determines oxidation product.

Isomer definition

Same molecular formula, different structure / arrangement. Ex: C4H10 n-butane vs isobutane.

Chain isomerism

Different carbon skeleton. Ex: n-butane CH3CH2CH2CH3 vs isobutane CH3CH(CH3)CH3.

Position isomerism

Different position of functional group or double bond. Ex: 1-butene CH2=CHCH2CH3 vs 2-butene CH3CH=CHCH3, 1-propanol vs 2-propanol.

Functional group isomerism

Different functional group. Ex: C3H6O: CH3CH2CHO propanal vs CH3COCH3 propanone, C2H6O: CH3CH2OH ethanol vs CH3OCH3 dimethyl ether.

Metamerism

Different alkyl groups around functional group (ethers, amines, ketones, esters). Ex: C2H5-O-C2H5 vs CH3-O-C3H7.

Tautomerism - Keto-Enol

Migration of α-H: keto C-C(=O)-C ⇌ enol C=C(OH)-C equilibrium, acid/base catalyzed. Ex: CH3COCH3 ⇌ CH2=C(OH)CH3.

Stereoisomerism

Same connectivity, different spatial arrangement. Ex: cis-2-butene vs trans-2-butene.

Conformational isomerism

Temporary isomers from rotation around sigma bond, cannot be isolated, Newman projection. Ex: ethane staggered vs eclipsed, staggered more stable by 12 kJ/mol.

Eclipsed vs Staggered vs Gauche

Staggered 60° dihedral most stable (torsional strain min), eclipsed least. For butane: anti 180° most stable, gauche 60° less stable than anti.

Cyclohexane conformations

Chair most stable, axial/equatorial, ring flip, boat less stable. Methyl equatorial more stable due to 1,3-diaxial strain.

Geometric isomerism cis-trans

From restricted rotation at C=C or ring, cis = same side, trans = opposite. Ex: cis-2-butene vs trans-2-butene.

E/Z nomenclature

Generalization of cis-trans with CIP priority: Z = Zusammen (same side), E = Entgegen (opposite). Ex: (Z)-but-2-ene = cis, (E)-but-2-ene = trans.

CIP Priority Rules

1) Higher atomic number higher priority 2) If tie, compare next atoms 3) Double bond counted as bonded twice. Order: -I > -Br > -Cl > -OH > -CH3 > -H.

Chirality

Non-superimposable on mirror image. Ex: hands, L-alanine.

Chiral center / Stereocenter

sp3 carbon with 4 different groups. Marked as C*. Ex: CHFClBr, CH3-CH(OH)-CH2CH3 2-butanol, CH3-CHCl-CH3? no.

Enantiomers

Mirror images, non-superimposable, same physical properties except optical rotation opposite. Ex: (R)- and (S)-lactic acid.

Diastereomers

Not mirror images, different physical properties. Ex: cis-trans is diastereomer, (R,R) vs (R,S) tartaric acid.

Racemic mixture

50:50 mixture of two enantiomers, optically inactive (external compensation). (±). Ex: (±)-lactic acid, rotation = 0.

Meso compound

Has internal plane of symmetry, achiral despite 2+ stereocenters, optically inactive (internal compensation). Ex: meso-tartaric acid (2R,3S).

Optical activity

Rotates plane-polarized light. (+) clockwise dextrorotatory, (-) counterclockwise levorotatory. Measured by polarimeter. Ex: (S)-(+)-lactic acid.

R/S absolute configuration

Assign CIP priorities, put lowest priority to back, 1->2->3 clockwise = R (Rectus), counterclockwise = S (Sinister). Ex: (R)-butan-2-ol.

Alkane general formula and properties

CnH2n+2, saturated, only sp3, non-polar, hydrophobic, bp increases with chain length, branching decreases bp.

Alkane combustion

CnH2n+2 + (3n+1)/2 O2 -> nCO2 + (n+1)H2O + heat. Ex: CH4 + 2O2 -> CO2 + 2H2O.

Free radical halogenation

Initiation: X2 -> 2X· (hv), Propagation: R-H + X· -> R· + HX, R· + X2 -> R-X + X·. Reactivity: F2>Cl2>Br2>I2, 3°>2°>1°. Ex: CH4+Cl2 --hv--> CH3Cl+HCl -> CH2Cl2 -> CHCl3 -> CCl4.

Cracking

Long alkane -> smaller alkane + alkene, high T, catalyst. Ex: C8H18 -> C4H10 + C4H8. Petroleum refining.

Alkene general formula

CnH2n, one double bond, sp2, planar around C=C, decolorizes Br2 water (orange -> colorless). Ex: C2H4 ethene. DoU=1.

Alkene addition reaction general

C=C + X-Y -> C(X)-C(Y). Pi breaks, sigma forms. Electrophilic addition. Pi acts as nucleophile.

Hydrogenation

C=C + H2 --Pt/Pd/Ni--> C-C alkane, exothermic, syn addition. Ex: CH2=CH2 + H2 -> CH3CH3.

Halogenation

C=C + X2 -> C(X)-C(X) vicinal dihalide, anti addition, decolorizes Br2. Ex: CH2=CH2 + Br2 -> CH2Br-CH2Br. Unsaturation test.

Hydrohalogenation Markovnikov

C=C + HX -> H attaches to carbon with more H, X to more substituted C, via most stable carbocation. Ex: CH3-CH=CH2 + HBr -> CH3-CHBr-CH3 major (2-bromopropane). Markovnikov rule.

Hydration acid-catalyzed

C=C + H2O --H2SO4--> alcohol, Markovnikov, carbocation intermediate. Ex: CH2=CH2 + H2O -> CH3CH2OH ethanol.

Polymerization

n alkene -> polyalkene. Ex: n CH2=CH2 -> -(CH2-CH2)n- polyethylene.

Alkyne general formula

CnH2n-2, one triple bond, sp linear, terminal H acidic. Ex: C2H2 ethyne HC≡CH, C3H4 propyne CH3C≡CH.

Terminal alkyne acidity

RC≡C-H pKa ~25 vs alkane pKa 50, alkene 44, due to sp 50% s character. Deprotonated by NaNH2 (pKa 36). RC≡CH + NaNH2 -> RC≡C- Na+ + NH3. Ex: HC≡CH + NaNH2 -> HC≡CNa.

Alkyne addition 2 equivalents

Triple can add 2 eq X2/HX/H2O. Ex: HC≡CH + 2Br2 -> CHBr2-CHBr2, HC≡CH + HBr -> CH2=CHBr, + HBr -> CH3-CHBr2 1,1-dibromoethane.

Cycloalkane general formula

CnH2n, ring = 1 DoU. Ex: C6H12 cyclohexane.

Ring strain theory

Small rings (3,4) have angle strain (Baeyer) 60° vs 109.5°, torsional, transannular. 6-membered most stable no strain. Stability: C3<C4<C5<C6.

Cis-trans in cycloalkanes

Ring restricts rotation, disubstituted cycloalkane shows cis (same side) trans (opposite). Ex: 1,2-dimethylcyclohexane cis vs trans.

Benzene formula and structure

C6H6, planar hexagon, 6 delocalized pi electrons, 2 Kekule resonance forms, bond length 140 pm intermediate between 154 and 134. Resonance energy 150 kJ/mol. Circle inside hexagon.

Hückel's Rule

Aromatic if cyclic, planar, conjugated, (4n+2) pi electrons. n=0,1,2… => 2,6,10,14… Antiaromatic if 4n. Ex: benzene 6pi n=1 aromatic, cyclobutadiene 4pi antiaromatic.

Aromaticity criteria

1) Cyclic 2) Planar 3) Conjugated p orbital at every atom 4) Hückel 4n+2. Ex: pyrrole C4H4NH, furan C4H4O, pyridine C5H5N also aromatic.

Resonance

Delocalization of pi electrons increases stability, real structure is hybrid of contributors. Ex: benzene circle.

Electrophilic Aromatic Substitution (EAS) general

C6H6 + E+ -> arenium ion (sigma complex) -> -H+ restores aromaticity. 3 steps: attack, deprotonation. Keeps aromaticity. C6H6 + E+ -> C6H5E + H+.

Nitration

C6H6 + HNO3/H2SO4 -> C6H5-NO2 + H2O, electrophile NO2+ nitronium ion. Ex: benzene -> nitrobenzene.

Halogenation of benzene

C6H6 + X2/FeX3 -> C6H5-X + HX, FeBr3 Lewis acid generates X+. Ex: C6H6 + Br2/FeBr3 -> C6H5Br bromobenzene. Different from alkene: needs Fe catalyst.

Sulfonation

C6H6 + H2SO4 (fuming, SO3) -> C6H5-SO3H + H2O, reversible, E+ = SO3. Ex: benzenesulfonic acid. Reversible = protecting group.

Friedel-Crafts Alkylation

C6H6 + R-Cl/AlCl3 -> C6H5-R + HCl, via carbocation, rearrangement possible, polyalkylation issue. Ex: C6H6 + CH3Cl/AlCl3 -> C6H5CH3 toluene.

Friedel-Crafts Acylation

C6H6 + RCOCl/AlCl3 -> C6H5-COR + HCl, acylium ion R-C≡O+ stable, no rearrangement, no poly. Ex: C6H6 + CH3COCl/AlCl3 -> C6H5COCH3 acetophenone.

Activating vs Deactivating groups

Activating (EDG) increases rate, o/p director: -OH, -NH2, -OCH3, -CH3, -C6H5. Deactivating (EWG) decreases rate: -NO2, -COOH, -CHO, -COR, -SO3H is m-director, except halogens -Cl,-Br deactivating but o/p.

Ortho/Para/Meta director explanation

Resonance: EDG donates e- stabilizes o/p sigma complex, EWG destabilizes o/p so m is favored. Ex: C6H5-OH o/p, C6H5-NO2 m.

Alcohol definition

R-OH, hydroxyl group attached to saturated sp3 carbon (not directly to aromatic ring; phenol is different). Ex: CH3OH methanol.

Classification 1° 2° 3° alcohol

By carbon bearing OH: 1° R-CH2-OH, 2° R2CH-OH, 3° R3C-OH. Determines oxidation product. Ex: CH3CH2OH 1°, (CH3)2CHOH 2°, (CH3)3COH 3°.

Nomenclature -ol

Suffix -ol, longest chain including OH, numbering gives OH lowest locant, prefix hydroxy- if higher priority group exists. Ex: CH3CH2OH ethanol, CH3CH(OH)CH3 propan-2-ol. Priority: -COOH > -CHO > -CO- > -OH.

Physical properties of alcohols

H-bonding -> high bp vs alkane/ether similar MW, small alcohols (C1-C3) miscible with water due to H-bond. Ex: C2H5OH bp 78°C vs C2H6 bp -89°C, vs CH3OCH3 -24°C.

Acidity of alcohols

Weak acid pKa ~16-18: R-OH -> RO- + H+, acidity: CH3OH > 1° > 2° > 3° (alkyl donates). Reacts with Na: 2ROH + 2Na -> 2RONa + H2, not with NaOH. Phenol pKa ~10 stronger.

Dehydration to alkene

ROH --conc H2SO4, 170°C--> alkene + H2O, E1 mechanism, more substituted alkene major (Zaitsev), reactivity 3°>2°>1°. Ex: CH3CH2OH --H2SO4--> CH2=CH2 + H2O.

Oxidation of alcohols

1° RCH2OH --[O]--> RCHO --[O]--> RCOOH (PCC stops at RCHO, Jones CrO3/H2SO4 goes to RCOOH), 2° R2CHOH --[O]--> R2C=O ketone, 3° R3COH no oxidation (no H). Ex: CH3CH2OH -> CH3CHO -> CH3COOH. [O]=K2Cr2O7/H+.

Reaction with HX to alkyl halide / Lucas test

ROH + HX (ZnCl2) -> RX + H2O, 3° immediate turbid, 2° 5-10 min, 1° no reaction at RT. Ex: ROH + HCl/ZnCl2 -> RCl + H2O.

Esterification

ROH + R'COOH --H2SO4--> R'COOR + H2O, Fischer esterification, reversible, acid-catalyzed. Ex: CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O.

Diols and Triols

Two OH = glycol, three OH = triol. Ex: HO-CH2-CH2-OH ethylene glycol, HOCH2-CHOH-CH2OH glycerol 1,2,3-propanetriol.

Ether definition

R-O-R', oxygen with two alkyl/aryl groups, no O-H. Ex: CH3-O-CH3 dimethyl ether, C2H5-O-C2H5 diethyl ether.

Nomenclature of ethers

Common: alkyl alkyl ether, IUPAC: alkoxyalkane. Ex: CH3OCH2CH3 = methoxyethane (ethyl methyl ether).

Physical and chemical of ethers

No H-bonding self, bp lower than alcohol similar MW, slight water solubility, relatively inert, good solvent, forms peroxides on standing (explosive), cleaved by HI/HBr: R-O-R' + HI -> ROH + RI, excess HI -> 2RI + H2O. Ex: Et2O bp 35°C anesthetic.

Peroxide formation

Ethers + O2 + light -> R-O-O-R peroxide explosive. Test with KI. Ex: Et2O + O2 -> peroxide. Old ethers dangerous to distill.

Amine definition and classification

R-NH2 primary, R2NH secondary, R3N tertiary. N with lone pair basic. 1° = one C attached to N. Ex: CH3NH2 methylamine 1°, (CH3)2NH dimethylamine 2°, (CH3)3N trimethylamine 3°. Amide ≠ amine.

Nomenclature of amines

Suffix -amine, prefix amino- if higher priority, common name aniline for C6H5NH2. Ex: CH3CH2NH2 ethanamine, C6H5NH2 aniline (benzenamine).

Basicity of amines

Lone pair on N accepts H+. Aliphatic amine pKb ~3-4 stronger than NH3, aromatic aniline pKb ~9.4 weaker due to resonance delocalization. Ex: CH3NH2 > NH3 > C6H5NH2. Basicity in water: R2NH > RNH2 > R3N > NH3 due to solvation, gas phase: R3N > R2NH > RNH2.

Physical properties of amines

1° and 2° can H-bond (N-H), higher bp than alkane, water soluble small amines, fishy smell. Ex: CH3NH2 gas, soluble.

Reactions of amines

Alkylation: RNH2 + RX -> R2NH -> R3N -> R4N+ X- (overalkylation). Acylation: RNH2 + RCOCl -> RNHCOR amide + HCl. With HNO2: 1° aliphatic -> N2 gas + mixture, 1° aromatic C6H5NH2 + NaNO2/HCl 0-5°C -> C6H5N2+Cl- diazonium salt (diazo coupling). 2° -> N-nitrosamine R2N-N=O yellow oil.

Aldehyde definition

R-CHO, carbonyl C=O with one H and one R, at end of chain, highly reactive. Ex: HCHO formaldehyde methanal, CH3CHO acetaldehyde ethanal.

General formula aldehyde

CnH2nO for aliphatic with one carbonyl, R-CHO. Same MF as ketone. Ex: C2H4O CH3CHO.

Nomenclature -al

Suffix -al, carbonyl C = C1, -carbaldehyde when CHO attached to ring. Ex: CH3CH2CHO propanal, C6H5CHO benzaldehyde = benzenecarbaldehyde. Priority: -COOH > -CHO.

Physical of aldehydes

Polar C=O, no H-bond self (no O-H), bp higher than alkane but lower than alcohol similar MW, small ones water soluble. Ex: HCHO gas soluble.

Oxidation of aldehydes

RCHO + [O] -> RCOOH. Tollens: Ag(NH3)2+ + RCHO -> Ag mirror (s) + RCOOH (aldehyde positive, ketone negative). Fehling/Benedict: Cu2+ -> Cu2O red precipitate (s) for aliphatic aldehyde (aromatic negative). Ex: RCHO + [O] -> RCOOH.