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This 20 page Class Notes was uploaded by Kristin Honowitz on Monday July 18, 2016. The Class Notes belongs to 101 at a university taught by Mr Teacher in Fall. Since its upload, it has received 14 views.
Reviews for MCAT___Organic_Chemistry_Overview.pdf
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Date Created: 07/18/16
Molecular Structure Valence Carbon – 4 bonds Nitrogen – 3 bonds Oxygen – 2 bonds Halogens – 1 bond Formal Charge = (Group #) – (# non‐bonding electrons) – (1/2 # bonding electrons) Index of Hydrogen Deficiency The NUMBER OF PAIRS of HYDROGENS required to become a SATURATED ALKANE For Resonance Structures ‐ Atoms must not be moved, only ELECTRONS MOVE Aromatic Molecules – (4n + 2) π electrons Hydrogen Bonding – occurs when HYDROGEN is bonded to a HIGHLY ELECTRONEGATIVE ATOM Conformational Isomers Not TRUE isomers – different spatial orientations of the same molecule Chirality‐ A chiral carbon is bonded to FOUR DIFFERENT SUBSTITUENTS Absolute Configuration Rectus (to the right) & Sinister (to the left) according to priority The LARGEST MOLECULAR WEIGHT is the HIGHEST PRIORITY (1) Hydrogen is always the lowest priority (4) and should be oriented out the back of the page Relative Configuration Two molecules have the SAME relative configuration about a carbon if they differ by only ONE SUBSTITUENT and the other substituents are oriented identically about the carbon Optical Activity & Observed Rotation Optically inactive compounds may have • No chiral centers & Equal amount of both stereoisomers (a racemic mixture) Optically Active compounds can be 1) + / d – rotates light CLOCKWISE 2) ‐ / l – rotates light COUNTER‐CLOCKWISE Structural Isomers 1) Same molecular formula 2) DIFFERENT BOND‐TO‐BOND CONNECTIVITY 3) Isobutane (C H ) vs. n‐butane (C H ) 4 10 4 10 4) Are NOT THE SAME MOLECULE Stereoisomer SUBTYPE ‐ Enantiomers 1) Same molecular formula 2) Same bond‐to‐bond connectivity 3) MIRROR IMAGES OF EACH OTHER 4) Are NOT THE SAME MOLECULE – opposite absolute configurations at chiral centers Same chemical and physical characteristics except for 1) Reactions with other chiral compounds 2) Reactions with polarized light Stereoisomer SUBTYPE ‐ Diastereomers 1) Same molecular formula 2) Same bond‐to‐bond connectivity 3) Are NOT MIRROR IMAGES OF EACH OTHER 4) Are NOT THE SAME MOLECULE Geometric Isomers (a special type of diastereomer) • Cis‐isomers & Trans‐isomers Meso Compounds 1) When TWO chiral centers OFFSET EACH OTHER 2) Optically Inactive 3) PLANE of SYMMETRY divides compound into two halves that are mirror images Stronger Dipole Moment Stronger Intermolecular Forces Higher Boiling Points Higher Energy Level – Higher Heat of Combustion Functional Groups Alkane H 3 – CH 3 Alcohol R – OH Alkene H 2 = CH 2 Ether R – O – R Alkyne HC ≡ CH Amine R – NH 2 R 2– NH R 3– N Aldehyde Ketone Carboxylic Acid Ester Amide Alkyl R Halogen [‐X] ‐F / ‐Cl / ‐Br / ‐I Hydroxyl ‐ G eminal ‐dihalide Alkoxy ‐ OR Vicinal ‐dihalide Hemiketal R | R | OR | OH Ketal R | R | OR | OR Hemiacetal H | R | OR | OH Acetal H | R | OR | OR Mesyl Group (M ‐ ) osyl Group (Ts‐) H | R | OR | OH Carbonyl Acyl Anhydride Aryl Benzyl Hydrazine Hydrazone Vinyl Allyl Nitrile Epoxide Enamine Imine Oxime Nitro Nitroso Hybridization Bond Angles Shape sp 180° Linear 2 sp 120° Trigonal Planar sp 109.5° Tetrahedral, Pyramidal, or Bent Hydrocarbons, Alcohols, & Substitutions Alkanes Methyl ‐CH Primary ‐CRH Secondary ‐CR H Tertiary‐CR 3 2 2 3 Lowest Density of all groups of organic compounds Methane, Ethane, Propane, and Butane are gases at room temperature INCREASED Molecular Weight | INCREASED Boiling Point | INCREASED Melting Point INCREASED Branching | DECREASED Boiling Point | INCREASED Melting Point Cyclo‐Alkanes CHAIR and BOAT conformations Large Substituents are RE STABLE in thEQUATORIAL POSITION Combustion (radical & exothermic reaction) CH + 2 O + energy CO + 2 H O + heat 4 2 2 2 COMBUSTION is a RADICAL REACTION HEAT OF COMBUSTION – change in enthalpy of a combustion reaction Halogenation (radical & exothermic reaction) Alkanes will react with HALOGENS in the presence of heat or light to form a FREE RADICAL HOMOLYTIC CLEAVAGE – bond is broken with one electron going with each atom 1) INITIATION a. Halogen is diatomic molecule, and HOMOLYTIC CLEAVAGE results in 2 free radicals 2) PROPAGATION a. HALOGEN RADICAL removes hydrogen from alkane, creating an ALKYL RADICAL b. ALKYL RADICAL reacts with diatomic molecule creating ALKYL HALIDE and a NEW HALOGEN RADICAL 3) TERMINATION a. TWO RADICALS BOND or RADICAL bonds to the wall of the container to end the chain reaction Stability of ALKYL RADICALS: 3° > 2° > 1° > methyl Fluorine – VERY REACTIVE, major product is PRIMARY Chlorine – REACTIVE, major product is whatever is LEAST STERICALLY HINDERED Bromine – SELECTIVE, major product is TERTIARY Dehydration of an alcohol (E1 Reaction) ‐ Alcohol + hot concentrated H SO Alkene + H O + HSO 2 4 2 4 Saytzeff Rule – MAJOR product of ELIMINATION is the MOST SUBSTITUTED ALKENE Dehydrohalogenation (E1 or E2 Reaction) E1 Mechanism – WITHOUT a strong base – 2 steps – unimolecular (substrate only) 1) Halogen drops off forming a CARBOCATION 2) Hydrogen is removed leaving alkene E2 Mechanism – STRONG BULKY BASE – 1 step – bimolecular (substrate & nucleophile) 1) Base REMOVES a hydrogen adjacent to the halogen 2) Halogen drops off leaving alkene In ELIMINATION, base pulls off a hydrogen In SUBSTITUTION, nucleophile attacks carbon Catalytic Hydrogenation (addition reaction) • Heterogeneous catalyst (Ni / Pd / Pt) promotes SYN addition • Hydrogenation is EXOTHERMIC with high energy of activation Oxidation Of Alkenes OZONOLYSIS – ozone is VERY reactive, breaking right through alkenes and alkynes Alkenes INTO two CARBONYL GROUPS Alkynes INTO two CARBOXYLIC ACIDS Electrophilic Addition Electrophiles – attracted to electrons –POSITIVELY CHARGED & Alkenes are ELECTRON‐RICH When HF / HCl / HBr / HI are added to an alkene: Markovnikov’s rule – the hydrogen will add to the carbon with the MOST HYDROGENS HBr & Peroxides (ROOR) add to alkenes ANTI‐MARKOVNIKOV Hydration of an Alkene Alkene + cold dilute H SO + H Alcohol 2 4 2 Oxymercuration / Demercuration 1) Oxymercurial ion attacks alkene, forming triangular mercury complex 2) H 2O attacks ANTI‐ to form aALCOHOL , losing the mercury group 3) IfROH is used instead of water,ETHER is formed Hydroboration Alkene + BH3 + peroxide Alcohol (anti‐markovnikov) Halogenation Of An Alkene Br andCl addANTI‐ to alkenes to forVIC‐DIHALIDES 2 Benzene • Undergoes SUBSTITUTION , not addition • Flat molecule, stabilized by RESONANCE • Ortho / Meta / Para Electron Donating Groups (ACTIVATES the Ring) STRONGLY donating (ortho‐ / para‐ directing) ‐O ‐ ‐OH ‐ NR 2 MODERATELY donating (ortho‐ / para‐ directing) ‐OR WEAKLY donating (ortho‐ / para‐ directing) ‐R Electron Withdrawing Groups (DEACTIVATES the Ring) STRONGLY withdrawing (meta‐ directing) ‐NO ‐ NR + ‐ CCl 2 3 3 MODERATELY withdrawing (meta‐ directing) ‐Carbonyls ‐ SO H CN 3 WEAKLY withdrawing (ortho‐ / para‐ directing) Halogens S N1 (substitution / nucleophilic / unimolecular 1) Hydrogen drops off forming a CARBOCATION – rate determining step 2) Nucleophile attacks the carbocation S N2 (substitution / nucleophilic / bimolecular 1) Nucleophile attacks substrate from behind – knocks leaving group free while binding to substrate Nucleophilicity A BASE is a stronger NUCLEOPHILE than its conjugate acid, but a BASE is NOT NECESSARILY a NUCLEOPHILE If a NUCLEOPHILE behaves as a BASE, ELIMINATION RESULTS LESS BULKY NUCLEOPHILE, with NEGATIVE CHARGE & POLARIZABILITY add to nucleophilicity Solvents POLAR PROTIC SOLVENTS – stabilize the nucleophile and any carbocation that forms INCREASE S 1 SNEED DECREASE S 2 SPNED POLAR APROTIC SOLVENTS – cannot form hydrogen bonds INCREASE S 2 SNEED DECREASE S 1 SPNED Leaving Groups The best leaving groups are those that are STABLE WHEN THEY LEAVE The WEAKER the BASE, the BETTER the LEAVING GROUP SN 1 vs. SN 2 SN1 SN2 Nucleophile N / A Strong Nucleophile Substrate 2° / 3° Methyl / 1 ° / 2° (unhindered) Solvent Polar solvent increases rate Polar solvent DECREASES rate Speed [Substrate] [substrate] [nucleophile] Stereochemistry Creates RACEMIC mixture INVERTS around chiral center Skeleton Maybe skeletal rearrangement NO rearrangement Alcohols BP goes up with increasing Molecular Weight ROH hydrogen bonds, dramatically raising MP and BP Alcohols can behave as ACIDS, with methyl –OH being the STRONGEST ACID Grignard Synthesis of Alcohols Oxidation Of Alcohols Oxygen‐Hydrogen ratio INCREASES – Oxidation occurred Oxygen‐Hydrogen ratio DECREASES – reduction occurred The Pinacol Rearrangement In VICINAL DIOLS, DEHYDRATION product is a KETONE or ALDEHYDE Ethers ALMOST ALWAYS THE ANSWER to SOLVENT QUESTIONS on the MCAT ROR + HBr ROH + RBr Acidities Of Functional Groups Alkane Alkene Hydrogen Ammonia Alkyne ALDEHYDE Alcohol Water CARBOXYLIC ACID Carbonyls & Amines The Carbonyl Carbon DOUBLE BONDED to oxygen PLANAR Stereochemistry PARTIAL POSITIVE on the carbon Aldehydes & Ketones ALDEHYDE R – = O ) – H KETONE R – (C=O) – R FORMALDEHYDE H – (C=O) – H ACETONE CH3 – (C=O) – CH3 Lower Boiling Point than ALCOHOL α‐carbon is VERY ACIDIC – loses a proton to become an ENOLATE ION (stabilized by resonance) In β‐dicarbonyls, the ENOLATE IONIC form is more prevalent KETO‐ENOL Tautomerization Formation of Acetals KETONE + ALCOHOL HEMIKETAL + ALCOHOL KETAL ALDEHYDE + ALCOHOL HEMIACETAL + ALCOHOL ACETAL Acetals / Ketals can act as BLOCKING GROUPS to PRESERVE a CARBONYL GROUP Aldol Condensation Aldehyde + Aldehyde Ketone + Ketone Aldehyde + Ketone α‐hydrogen is abstracted, forming an ENOLATE ION α‐carbon of ENOLATE attacks carbonyl carbon of other molecule, forming ALKOXIDE ION ALKOXIDE ION grabs a hydrogen to become an ALDOL (aldehyde & alcohol) Halogenation & Haloform Reaction HALOGENS add to KETONES at the α‐carbon in presence of acid or base METHYL KETONE with BASE, the α‐carbon is COMPLETELY HALOGENATED HALOFORM breaks off (CHCl / CHBr 3 / CHF ) leaving CARBOXYLATE ION Wittig Reaction Ketone / Aldehyde + Ylide (carban i o nALKENE α‐β Unsaturated Carbonyls Also called 1,4‐addition – adding HX forms ENOL TAUTOMER and then KETO Carboxylic Acids Carboxylic Acid R‐COOH Formic Acid H – COOH Benzoic Acid C6H ‐ COOH Acetic Acid CH 3 – COOH If the name ends in –ate R – COO‐ Make STRONG HYDROGEN BONDS – to form dimmers This effectively doubles M.W. – significantly increasing B.P. Decarboxylation CARBOXYLATE ION LOSES CO 2 to become KETO‐ENOL TAUTOMERS Carboxylic Acid Derivatives – ACYL CHLORIDES MOST REACTIVE OF ALL CARBOXYLIC ACID DERIVATIVES ACID CHLORIDE + H2 CARBOXYLIC ACID + HCl ACID CHLORIDE + RO H ESTER + HCl ACID CHLORIDE + RN H MIDE + HCl ACID CHLORIDE + RCOOH ANHYDRIDE + HCl ACID CHLORIDE + H2 CARBOXYLIC ACID + HCl ESTER + H2 CARBOXYLIC ACID + ROH AMIDE + H2 CARBOXYLIC ACID + RNH2 ANHYDRIDE+ H2 CARBOXYLIC ACID + RCOOH ALDEHYDES / KETONES Nucleophilic ADDITION CARBOXYLIC ACIDS / DERIVATIVES Nucleophilic SUBSTITUTION Carboxylic Acid Derivatives ‐ ESTERIFICATION Carboxylic Acid Derivatives ‐ TRANSESTERIFICATION Carboxylic Acid Derivatives – ACETOACETIC ESTER SYNTHESIS ACETOACETIC ESTER + RX + H+ / HEA T KETONE + CO 2 Carboxylic Acid Derivatives ‐ REACTIVITIES Amide Ester Carboxylic Acid Acid Anhydride Acyl Chloride Amines Ammonia ‐ NH 3 Amine Degree depends on number of ATTACHED –R GROUPS 1) Act as LEWIS BASE – DONATING LONE PAIR OF ELECTRONS 2) Act as a NUCLEOPHILE where LONE PAIR of ELECTRONS attacks POSITIVE CHARGE 3) Nitrogen can take on a FOURTH BOND (+) 4) Nitrogen can HYDROGEN‐BOND – increasing BOILING POINT and SOLUBILITY Condensation with Ketones AMINE + ALDEHYDE / KETONE WATER + IMINE / ENAMINE Wolff‐Kishner Reduction HYDRAZINE + ALDEHYDE / KETONE ALKANE + WATER + N 2 Alkylation of Amine Hofmann Elimination Amines & Nitrous Acid NITROUS ACID + 1° AROMATIC AMINE DIAZONIUM ION The Diazonium Group is EASILY REPLACED Amides Acetamide N ‐ethylacetamide β‐Lactams (CYCLIC AMIDES) Hofmann Degradation Phosphoric Acid When heated, phosphoric acid forms PHOSPHORIC ANHYDRIDES Tri‐phosphates exist as negative ions, such as ATP Biochemistry & Lab Techniques Fatty Acids LONG CARBON CHAIN WITH COOH on the end Amino Acids Zwitterion – DIPOLAR ION (one side – and one side +) BASIC AMINO ACIDS Histidine Arginine Lysine ISOELECTRIC POINT – the pH where 100% of the amino acids are ZWITTERIONS Carbohydrates 1) GENERAL FORMULA C (H O) n 2 n 2) Can have either ALDEHYDE or KETONE groups to be called ALDOSE or KETOSE 3) ANOMERIC CARBON – the ONLY CARBON attached to TWO OXYGENS Lab Techniques SPECTROSCOPY • Nuclear Magnetic Resonance (NMR) • Infrared Spectroscopy (IR) • Ultraviolet Spectroscopy (UV) SPECTROMETRY • Mass Spectrometry SEPARATION TECHNIQUES • Chromatography • Distillation • Crystallization • Extraction NMR 1) Each peak is a CHEMICALLY‐EQUIVALENT HYDROGEN 2) SPLITTING PEAKS is created by NEIGHBORING HYDROGENS as by n+1 (n = # of neighboring carbons) 3) To the LEFT is DOWNFIELD (unshielded by electronegative atoms) IR Spectroscopy CARBONYL GROUP 1700 ‐OH GROUP 3200 – 3600 Ultraviolet Spectroscopy UV starts around 220 nm (butadiene) 1) Each additional CONJUGATED BOND adds 30‐40 nm to the wavelength ABSORBED MOST Visible Spectrum • If compound has 8+ CONJUGATED DOUBLE BONDS, its absorbance enters the VISIBLE SPECTRUM • β‐Carotene has 11 CONJUGATED DOUBLE BONDS, with an absorbance of about 500 nm • β‐Carotene absorbs the BLUE‐GREEN color of 500 nm, and displays the COMPLEMENTARY COLOR of red‐ orange Mass Spectrometry • Mass Spectrometry gives the MOLECULAR WEIGHT • Sample molecules are bombarded by electrons, causing them to break apart and IONIZE • Ions are accelerated through a magnetic field, most are +1 • RADIUS OF CURVATURE depends upon the MASS to CHARGE RATIO (m/z) • BASE PEAK – the largest peak • PARENT PEAK – the peak made by the molecular ion (same as ORIGINAL MOLECULE but without ONE ELECTRON so it has a +1 charge) Chromatography • Separation of a mixture by passing it over or through a matrix that ADSORBS different compounds with DIFFERENT AFFINITIES • MOBILE PHASE / STATIONARY PHASE • The MORE POLAR compound moves more SLOWLY because it binds to the POLAR STATIONARY PHASE Distillation • Separation based upon VAPOR PRESSURE • Separates a solution of two volatile liquids with a BOILING DIFFERENCE of at least 20° C • The compound with the LOWER BOILING POINT (HIGHER VAPOR PRESSURE) will boil off and can be captured Crystallization • Works on the principle that PURE SUBSTANCES FORM CRYSTALS more easily than impure substances • Crystallization is VERY INEFFICIENT Extraction • Based on SOLUBILITY DUE TO SIMILAR POLARITIES • LIKE DISSOLVES LIKE
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