Organic Chemistry Flashcards
Blueprint MCAT Prep
IUPAC Nomenclature for Alkanes
(1) Identify and name longest carbon chain (1C = Methane, 2C = ethane, 3C = propane, 4C = butane, 5C = pentane, etc.)
(2) Label carbons such that substituents have lowest possible #’s
(3) Identify all substituents (methyl, ethyl, etc.)
(4) Place substituents in alphabetical order
Priority of Substituents in IUPAC Nomenclature of Alkanes
Other functional groups have a suffix (when they are the highest-priority group): -COOH (-oic acid) is highest priority, followed by carboxylic acid derivatives, aldehydes/ketones (suffix: -al/-one, prefix: oxo-), alcohols (suffix: -ol, prefix: hydroxy), amines (suffix: -amine, prefix: amino-), thiols (suffix: thiol, prefix: mercapto-), and hydrocarbons
Resonance
When more than one equivalent Lewis structure can be drawn for a compound. Multiple structures indicate electron delocalization.
Aromatic Compounds
Conjugated cyclic molecules with planar structure + satisfy Huckle’s rule: having 4n + 2 pi electrons, where n is 0 or an integer
Cahn-Ingold-Prelog Rules for assigning priority to substituents
(1) Look at atoms directly connected to the stereocenter; heavier atoms have higher priority
(2) If two atoms are the same, move one atom further down the substituents and re-rank by substituents.
(3) Continue until a difference is encountered; multiple bonds are higher-priority than single bonds
E/Z System for double bonds
E if higher-priority substituents are on opposite sides of double bond, Z if higher-priority substituents are on the same side
R/S System for chiral system
Orient molecule such that lowest-priority substituent faces into the page and connect substituents from high to low priority; if doing so traces a clockwise pattern
Molecule is R; if counterclock-wise, S
Chirality
Non-superimposable mirror images (enantiomers)
C must have 4 different substituents. When there is more than one chiral center, enantiomers have opposite orientation at all chiral centers, while diasteromers only differ at some
For n chiral centers, there is a maximum of 2^n stereoisomers
Alcohol
RC - OH
-ol, hydroxy-
High melting/boiling point
Aldehyde
RC(O)H
-al, oxo-
Ketone
R(C=O)R’
-one, oxo-, keto-
Carboxylic Acids
-oic acid
R(C=O)OH
High melting/boiling point
Amide
R(C=O)NH2
-amide
Ester
R(C=O)OR’
-yl, -ate
Acid Anhydride
R(C=O)O(C=O)R’
-oic anhydride
Amine
R-NH2, R-NHR
-amine, amino-
Imine
R=NH, R=NR’
Enamine
RC=CNH, C=CNHR
Mild Oxidizing Agents
PCC
Strong Oxidizing Agent
NaCr2O7, K2Cr2O7, and CrO3
Mild Reducing Agent
NaBH4
Strong Reducing Agent
LiAlH4
Factors Affecting Acidity
Resonance
Factors Affecting Reactivity
Electron-withdrawing groups, resonance, steric effect, strain
Basic Idea for a Mechanism
An electrophile and a nucleophile form a bond
Electrophile
An atom that ‘needs’ electrons (usually has positive or partial positive charge)
Nucleophile
An atom that ‘needs’ to share its excess electrons (usually has negative or partial negative charge
Sn1
Nucleophilic substitution with a first-order rate law (depends on substrate concentration only). Carbocation forms, then nucleophile attacks.
Favorable Factors: highly substituted carbons, polar protic solvent
Sn2
Nucleophile substitution with a second-order rate law (depends on substrate and nucleophile concentration). Nucleophile performs ‘backside attack’ and kicks out leaving group, inverting the stereochemestry
Favorable Factors: Methyl/primary carbons, strong and non-bulky nucleophile, polar aprotic solvent
Carboxylic Acid
C has a strong partial positive charge, is a good electrophile. Nucleophilic substitution is common, as in Fischer esterification and imine formation
Nucleophile Attacks carboxylic acid C, then leaving group is kicked off
Nucleophilic Addition At Carbonyl C (C=O)
Hemiacetals (-R, -H, -OH, -OR’) formed from aldehydes, hemiketals (-R, -R’, -OH, -OR’’) from ketones. Reaction can repeat with excess alcohol to form acetals and ketals (another -OR group instead of -OH)
Nucleophile attacks carbonyl C without a leaving group
Keto-Enol Tautomerism
Can be catalyzed by acid or base, a-hydrogen removal is critical in both (first step in base-catalyzed mechanism, second step in acid catalysis)
Enolate Chemistry
Resonance-stabilized negative charge on a-carbon allows carbon to be a nucleophile
Aldol Condensation
Nucleophilic a-carbon attacks electrophilic carbonyl C to form a new C-C bond
Retro-Aldol
Reverse of the aldol condensation process
Michael Addition
An Enolate attacks the B-carbon of an a,B-unsaturated aldehyde/ketone
Robinson Annulation
Michael addition followed by aldol condensation
Analytic Techniques
Identify features of a molecule or the molecule’s identity
- Often render the sample unusable in the future
- Examples: IR, NMR, UV-Vis, mass spec.
Separation Techniques
Convert a mixture into multiple separate, pure samples (to the extent to which this is possible)
- Samples can then be analyzed or otherwise used later
- Examples: Distillation, extraction, chromatography, recrystallization, filtration
Infrared (IR) Spectroscopy
Uses radiation with a frequency lower than that of visible light to vibrate bonds
C=O –> 1700 cm-1, sharp
O-H –> 3200-3600 cm-1, broad
Nuclear Magnetic Resonance (NMR) Spectroscopy
Left side of spectrum = “downfield” = deshielded = close to e- withdrawing groups
Right side of spectrum = “upfield” = shielded = far from e- withdrawing groups
Area under peak corresponds to number of equivalent hydrogens
Splitting (singlet, doublet, … etc.) is determined by number of hydrogens on adjacent atom
Ultraviolet-visible (UV-Vis) Spectroscopy
Useful to discern presence of conjugated/aromatic species
Mass Spectroscopy
Helps determine molecular weight (m/z peak)
Distillation
Separates liquids based on boiling point (BP)
- For BPs > 25° apart, use simple distillation
- For BPs < 25° apart, use fractional distillation
- For very high BPs, use vacuum distillation to lower atmospheric pressure (lower P = lower BPs)
Extraction
Separates liquids based on solubility/acid-base properties
- Requires immiscible aqueous and organic layers in a seperatory funnel
- To send an acid into the aqueous layer, add base (deprotonate it)
- To send base into the aqueous layer, add acid (protonate it)
Chromatography
Involves a mobile phase and a stationary phase with different properties
TLC
Stationary phase is polar (usually silica) while mobile phase is a nonpolar solvent
Rf = (distance traveled by compound) / (distance traveled by solvent)
Other forms of Chromatogrphy
Size-exclusion, cation-exchange, anion-exchange, and affinity chromatogrphy are all forms of column chromatography
Gas Chromatography
Vaporizes sample and passes through a column, then measures retention time
HPLC
Rapid method of column chromatography; polar stationary phase and nonpolar mobile phase for regular process; nonpolar stationary phase and polar mobile phase for reverse process (RP-HPLC)
Other Separation Techniques
Recrystallization and Filtration
