Kaplan Organic Chemistry Unknown Concepts Flashcards
What is the order of alkane naming?
methane
ethane
propane
butane
pentane
hexane
List the priority of functional groups in decreasing order.
1) carboxylic acids
2) anhydride
3) esters
4) amides
5) aldehyde
6) ketone
7) alcohol
8) thiol
9) amine
10) alkenes, alkynes, alkanes
** this is by oxidation #
What are the most important commonly named compounds to know for the MCAT?
ethyl alcohol, isopropyl alcohol
formaldehyde (1C), acetaldehyde (2C), propionaldehyde
formic acid (1C), acetic acid (2C), propionic acid (3C)
What is the difference between physical and chemical properties?
physical: no change in composition of matter; melting point, boiling point, solubility, odor, color, density
chemical: reactivity of molecule, resulting in change in composition; generally attributable to functional groups in the molecule
What is optical activity? How is it labeled?
rotation of plane-polarized lights by a chiral molecule
- rotates to the right, clockwise = d, +
- rotates to the left, counterclockwise = l, -
racemic mixtures and meso compounds (internal plane of symmetry) display no optical activity
How do you calculate specific rotation?
[alpha] = alpha-obs / c x l
alpha = specific rotation
c = concentration in g/mL
l = length of tube in dm (1 cm = 0.1 dm)
What is the formula to calculate the possible # of stereoisomers?
2^n, where n is the # of chiral carbons
What is resonance?
delocalization of electrons in molecules with conjugated bonds = single and multiple bonds alternate, creating a system of unhybridized p-orbitals where pi electrons can delocalize
increases stability of the molecule
What is a Lewis acid and Lewis based? Bronsted?
Lewis acid: accepts electrons
Bronsted acid: donate proton
Lewis based: donates electrons
Bronsted base: accept proton
amphoteric = acid or base
How do you calculate the Ka? pKa?
pKa = -log Ka = -log [H+][A-]/[HA]
SMALL pKa = more acidic
- below -2 = strong acid
What makes a good nucleophile?
negative charge, pi bonds, or atoms with lone pairs of electrons
- EDG helps
charge: increases with increasing electron density
electronegativity: decreases with increasing electronegativity
steric hindrance: bulkier molecules are less nucleophilic
solvent: protic solvents can hinder by protonating the nucleophile or through H-bonding
How does the solvent affect nucleophilicty?
polar, protic (water, alcohols, ammonia, carboxylic acids): nucleophilicty increases and you move down the periodic table because the acid gets stronger, not as affected by protonation
polar, aprotic (DMF, DMSO, acetone): nucleophilicity increases as you move up the table
What makes a good electrophile?
more positive compounds are more electrophilic; being attached to electronegative atoms helps (EWG)
anhydrides most reactive (carboxylate anion is an excellent LG)> carboxylic acids > esters > amides
What is the difference between acid/base and nucleophilic/electrophilic reactions?
acidity/basicity is measured by position of equilibrium in protonation or deprotonation = thermodynamic
nucleo/electro are based on relative rates of rxns, so are KINETIC
What makes a good LG?
able to stabilize electrons
- I-, Br-, Cl-
- resonance
alkanes never LG because they form reactive anions
Describe Sn1 vs. Sn2 reactions.
Sn1: 2 steps, first is rate limiting, depends on the concentration of the substrate k = [substrate]
1) LG leaves, creating a carbocation (more substituted, the better)
2) Nu attacks
product is racemic mixture
Sn2: one step; Nu attacks compound as the LG leaves
- concerted rxn
- strong nucleophile, no steric hindrance
- rate = k[substrate][Nu]
inverts stereochemistry = R to S
What are common oxidizing agents?
getting reduced, accepting electrons: Cr6+ (chromate), O2/O3/Cl2, Mn7+ (permanganate)
alcohols –> aldehydes (PCC stops here) –> carboxylic acid (CrO3, Cr2O7 2+)
increase the # of bonds to oxygen
- CO2 most oxidized, CH4 most reduced
- most oxidized carbons tend to be most reactive
What are common reducing agents?
donate electrons: metal + large # of hydrides: LiAlH4, NaBH4
aldehyde –> 1 alcohol
ketone –> 2 alcohol
What are diols commonly used for in reactions?
protecting groups, bond to ketones before redox
- acid work up removes them
What is the most acidic alcohol? How does the presence of other groups affect this alcohol?
phenol: aromatic nature of the ring allows for resonance stabilization of the negative charge on oxygen
- EWG: increase acidity
- EDG: decrease acidity; alkyls
What does PCC (pyridinium chlorochromate)?
oxidizes PRIMARY alcohols to aldehydes
- stops here, does not continue to CA
What are quinones? hydroxyquinones? ubiquinone (Coenzyme Q)?
oxidation of phenols
hydroxyquinones: reduction of quinones, adding variable # of hydroxyl groups
CoQ: electron acceptor of the ETC; reduced to ubiquinol (carry 2 e-, 2H+, carries to Complex III, unloads)
How do you determine the hybridization of an atom?
atoms + lone pairs
4: sp3
3: sp2
2: sp
Describe the characteristics of alpha-hydrogens of a carbonyl carbon. What happens when a strong base is added?
relatively acidic and can be removed with a strong base
- EW oxygen weakens the CH bond on the alpha carbon
- enolate resulting from deprotonation can be stabilized with resonance
Are ketones more or less reactive towards nucleophiles?
less: steric hindrance from extra alkyl group, which also donates electron density to the carbanion, making it less stable
What are the physical properties of CA?
polar and H-bond very well–> high BP
often exist as dimers in solution
acidity is enhanced by resonance between oxygen atoms
B-dicarboxylic acis have a highly acidic alpha hydrogen
What is soap?
mixing long-chain CA with strong base = carboxylate + Na+ + long FA chain
“saponification”
- form micelles to dissolve hydrophobic material in the interior
Rank the reactivity of carboxylic acid derivatives
anhydrides (resonance, 3 EWG) > esters > amides (ED amino group)
What factors affect reactivity?
1) steric hindrance
2) induction: distribution of charge across sigma bonds
- more EN, dipole creation, more positive character
3) conjugation and resonance: alternating single and multiple bonds creates delocalized pi electron clouds above and below the plane of the molecule
- more reactive because they can stabilize transition state
4) stain: increases reactivity
Describe what happens in anhydride cleavage reactions.
1) add NH3, cleaves anhydride into amide + CA
2) add ROH, cleaves anhydride into ester + CA
3) add H2O, cleaves anhydride into 2 CA
What is transesterification?
using an alcohol to exchange an ester group on a CA
What happens in strong acid or strong base to an amide?
hydrolysis; CA + amine
Describe the stereochemistry of amino acids and the exceptions.
all amino acids are L-amino acids
they all have S stereochemistry exceptive cysteine, which is R
Describe Strecker synthesis.
generates amino acid from an aldehyde converted into an aminonitrile
aldehyde (electrophile), mixed with NH4Cl (nucleophile 1) and KCN (nucleophile 2), H2O (nucleophile 3)
Describe Gabriel synthesis.
generates amino acid from potassium pthalimide (nucleophile), diethyl bromomalonate (electrophile 1), and alkyl halide (electrophile 2)
- two Sn2 reactions, hydrolysis, and decarboxylation
Compare Strecker to Gabriel synthesis.
both result in racemic mixture of amino acids
Strecker: condensation reaction, nucleophilic addition, hydrolysis
Gabriel: two Sn2 reactions, hydrolysis, and decarboxylation
What is inorganic phosphate? Where is phosphate found?
phosphate buffer = mixture of HPO42- and H2PO4-
phosphodiester bonds in backbone of DNA
- PPi is released in forming these bonds
What are phosphate bonds high energy?
large negative charges in adjacent phosphate groups and resonance stabilization
What is the buffering capacity of phosphoric acid?
three hydrogens with unique pKa allows for wide range of pH buffering ability
What does infrared spectroscopy measure (IR)?
absorption of infrared light, which causes molecular vibrations that must change dipole moment
1) plotted as percent transmittance vs. wavenumber (1/lambda (wavelength))
- fingerprint region is between 1500 and 400 cm-: contains peaks used to identify compound
- O-H peak, broad: 3300, CA = 3000
- N-H peak, sharp: 3300
- C=O peak, sharp: 1750
functional groups
What does ultraviolet (UV) spectroscopy measure?
absorption of UV light, which causes movement of electrons between orbitals
1) plotted as percent transmittance vs. wavelength
- to appear, has to have a small energy difference between HOMO and LUMO to permit electron movement
double bonds or heteroatoms with lone pairs that create conjugated systems
What does nuclear magnetic resonance (NMR) spectroscopy measure?
measure alignment of nuclear spin with an applied magnetic field (MRI)
- structure + connectivity of a compound
1) plotted as frequency vs. absorption of energy
- higher chemical shifts are DOWNFIELD (left)
- lower chemical shifts are UPFIELD (right)
What is the most common type of NMR spectroscopy?
Proton (1H) NMR
- each unique group of protons has its own peak
- AUC of peak is proportional to # of protons
- deshielding occurs when EWG pull electron density away from the nucleus, moving peak downfield
- when H are on adjacent atoms, splitting occurs: n+ 1, where n is the number of adjacent hydrogens
- alkyl groups: 0-3 ppm
- alkynes: 2-3 ppm
- alkenes: 4-6 ppm
- aromatic H: 6-8 ppm
- aldehyde H: 9-10 ppm
- CA H: 10-12 ppm
DO NOT COUNT PEAK AT 0 = TMS
determining # of protons
What is extraction?
combines two immiscible (don’t mix) liquids, one of which easily dissolves the compound of interest
- polar layer = aqueous phase and dissolves compounds with H bonding or polarity
- nonpolar layer = organic phase and dissolves nonpolar compounds
collected in funnel, one phase collected, solvent evaporated
What is the opposite of extraction?
wash: small amount of solvent that dissolves impurities is run over the compound of interest
What is filtration?
isolates a solid (residue) from a liquid (filtrate)
- gravity = filtrate
- vacuum = solid
What is recrystallization?
product is dissolved in a minimum amount of hot solvent and let it crystallize as it cools
- only the product is soluble at high temps
What is distillation?
separates liquids according to differences in their boiling points; vaporizes first is the distillate
What are the different types of distillation?
Simple: boiling points under 150 and are at least 25 degrees apart
Vacuum: bp over 150
Fractional: bp are less than 25 apart
What are the phases in chromatography?
stationary: usually polar solid
mobile: runs through the stationary phase and is usually liquid or gas
compounds with higher affinity for stationary phase have higher retardation factors and take longer to pass
What are thin-layer, paper and reverse-phase chromatography?
thin-layer/paper = polar stationary (silica) and nonpolar solvent that climbs through capillary action
- polars dont move as far
reverse-phase uses nonpolar card with polar solvent
- nonpolar dont move as far
What is column chromatography?
stationary phase = column containing silica or alumina beads
mobile = nonpolar solvent
ion-exchange = coated with charge to bind molecules with opposite charge
size-exclusion = small pores trap smaller compounds
- larger pass through
affinity = receptor or antibody to the compound
What is gas chromatography?
separates vaporizable compounds
- stationary phase = crushed metal or polymer
- mobile = nonreactive gas
What is HPLC?
better version of column chromatography with high pressure for a liquid sample
