Organic Chemistry Flashcards
Characteristics of Alcohols
R-OH
- functional group is -OH
- H-bonding results in both elevated boiling point and better solubility.
- Weakly acidic
R(=O)H
Aldehyde
R(=O)R
Ketone
R-O-R
Ether
(CH3)3 - C
t-butyl
(CH3)3-CH2-C
neopentyl
(CH3)2-CH
isopropyl
R(=O)-OH
Carboxylic Acid
R(=O)-OR
Ester
R(=O)-X
Acyl Halide
R(=O)-NH2
Amide
CH3-CH2-CH(CH3)
sec-butyl
RC(triple bond)N
cyanide/nitrile
CH2-CH(CH3)2
isobutyl
Alkanes
Cn H2n+2
Fully saturated hydrocarbons consisting of hydrogen/carbon joined by single bonds.
C1-C4: gases, C5-C15: liquids, longer: waxes and harder solids.
increase in chain length = increase in bp, mp, and density.
increase in branching = decrease in all three above.
Alkenes
Cn H2n (double bond) olefins”
Alkynes
Cn H2n-2 (triple bond)
Physical properties are similar to alkenes and alkanes.
Shorter = gases, boiling at high T than alkenes.
Nomenclature
- Multiple bonds should be on backbone.
- -OH is high priority (placed above multiple bond)
- Haloalkanes, ethers, and ketones are often given common names (e.g. methyl chloride, diethyl ketone)
- Aldehydes/carboxylic acids are terminal functional groups
- Specify isomer, if relevant (such as cis/trans, R or S, etc).
Isomers
Chemical compounds that have same molecular formula, but differ in structure.
May be extremely similar or extremely different.
Structural Isomers
Share only their molecular formula, but their atomic connectivity is different.
Therefore, they may have very different chemical and physical properties.
Stereoisomers
Have same atomic connections, but the atoms are arranged differently in space.
Examples:
Geometric isomers, Enantiomers, Diastereomers, Meso Compounds, and Conformational.
Chirality
Carbon atoms have four different substituents.
Geometric Isomers
Differ in position of substituents attached to a double bond.
Cis (Z) - Substituents on same side (based on high atomic number)
Trans (E) - Substituents are on opposite sides.
Enantiomers
Chiral objects that are non-superimposable mirror images.
Specific type of stereoisomers.
Absolute Configuration
(R) and (S) notation.
- Think of a steering wheel.
- Lowest priority substituent is in fourth position and should point away from you, down the column.
- While #1, 2, and 3 lie on the wheel itself.
- R is clockwise, and S is counterclockwise.
Fischer Projection
Horizontal lines indicate bonds that project from plane of page, while vertical lines behind plane of page.
Racemic mixture
Mixture of equal concentrations of both the (+) and (-) enantiomers.
Rotations cancel each other out, thus NO optical activity.
Diastereomers
Differ in chirality, but are NOT mirror images.
For any molecule with n chiral centers, there are 2^n possible stereoisomers.
e.g. Compound with 2 chiral centers = 4 stereoisomers.
Meso Compounds
Have a mirror image that is superimposable.
Thus, NOT optically active.
Have a mirror plane of symmetry
Conformational Isomers
Differ only by rotation about one or more single bonds.
Analogous to a person sitting or standing.
Can be seen in Newman projection.
Newman Projection
Line of sight extends along a carbon carbon bond axis. (Gauge, anti, eclipsed versions)
Straight-Chain Conformations
gauche < eclipsed < totally eclipsed
anti isomers have lowest energy
totally eclipsed have highest energy
At RT these easily interconvert
Cyclic Conformations
Strain Energy is due to ring strain, angle strain, torsional strain, and nonbonded strain (van der waals)
Chair and boat conformations are most important forms of cyclohexane. Chair is most stable and lowest energy.
Axial Substituents
Axial substituents are on Vertical Axis, like axial skeleton.
Axial is NOT favored.
Equatorial Substituents
Equatorial substituents go around the middle, like earth’s equator.
Equatorial is favored over axial.
A bulky substituent can prevent the ring from adapting certain conformations.
Hybridization
Concept of mixing atomic orbitals to form new hybrid orbitals.
Useful in explanation of shape of molecular orbitals.
Bonding Summary (single, double, and triple bonds)
Single bonds: sigma, sp^3, 109.5 degrees
Double bonds: sigma/pi, sp^2, 120 degrees
Triple bonds: sigma/pi/pi, sp, 180 degrees
Free Radical Halogenation
One or more H atoms are replaced by halogen atoms (Cl, Br, or I) via free radical substitution. Occurs in Alkanes.
Three steps:
- Initiation
- Propagation
- Termination
Bromine is slow and picky and attacks most substituted.
Chlorine is rapid and attacks primary H with abundance.
Combustion
Occurs in Alkanes.
Reaction of alkanes with molecular oxygen.
Forms CO2, Water, and Heat (desired product)
Pyrolysis
Occurs in Alkanes.
Also called cracking”.
Nucleophilic Substitutions
Occurs in Alkanes.
Nucleophiles are electron rich species that attracted to positively polarized atoms.
Basicity: Stronger the base, stronger the nucleophile.
Size/polarizability: dependson solvent. Protic = larger atoms. Aprotic = more basic atoms are better.
Best Leaving Groups
I > Br > Cl > F
Weak bases make good leaving groups.
Can accept electron pair and dissociate to form stable species.
Sn1 Reactions
Rate is dependent on ONE species.
Rate determining step is the carbocation.
Favored in POLAR protic solvents (water or acetone)
rate = k[RX]
Want stable carbocations: 3 > 2 > 1 > CH3 (favored with use of bulky nucleophiles)
Produces Racemic products (lose optical activity)
Leaving group = weak bases are best.
Sn2 Reactions
ONE step (no carbocation)
rate = k[Nu][RX] (substrate and nucleophile)
Usually attacks from the backside.
Best Reactant: 1 > 2 > 3
Favored in polar APROTIC solvents.
Optically active and inverted products.
Need strong nucleophile and transition state.
Elimination Reactions
Used in synthesis of alkenes.
Elimination reactions of either alcohols or alkyl halides.
In these reactions, the carbon skeleton loses HX (X = halide) or a molecule of water, to form double bond.
Two types E1 and E2
Unimolecular Elimination (E1)
TWO step process, proceeding through a carbocation intermediate.
k = [RX] (substrate)
Elimination of leaving group plus proton = double bond.
- Leaving group departs, producing carbocation.
- Proton is removed by a base.
E1 is favored by same factors as SN1: highly polar solvents, Weak Nu, highly branched carbon chains (3), and good leaving groups.
However, HIGH temps favor E1.
Bimolecular Elimination (E2)
ONE step process.
k = [RX][Base]
Strong base such as ethoxide ion (C2H5O-) removes a proton, while halide ion anti to proton leaves = double bond.
Often two possible products, but more substituted preferred.
Steric hindrance does NOT affect E2.
Strong base favors E2 over SN2.
SN2 favored over by E2 by weak Lewis bases. (Strong Nu)
Catalytic Hydrogenation
Reductive process of adding hydrogen to a double bond with aid of a metal catalyst. (platinum, palladium, and nickel)
Product: Alkane with syn addition of H.
Reaction takes place on metal surface, thus H atoms are added to same face (syn addition).
Addition of HX
An electrophilic addition that occurs in alkenes.
Electron of double bond acts as Lewis base and reacts with electrophilic HX molecules.
- Yields carbocation after double bond reacts with H+
- Halide ion combines with carbocation to give alkyl halide.
Follows Markovnikov rule (add to the most substituted carbon)
Product: Alkyl halide
Addition of X2
Addition of halogens to double bond.
Rapid process.
Nucleophile is the double bond, which attacks an X2 molecule, displacing X-.
Forms intermediate cyclic halonium ion, which is then attacked by X- to make a dihalo compound.
Anti-addition (attacks SN2).
Product: dihalo alkane
Addition of H20
Water can be added to alkenes under acidic conditions.
Protonated according to markovnikov.
Performed at LOW temperatures.
Product = alcohol
Free radical Additions
Alternate mechanism for addition of HX to double bond.
Occurs when PEROXIDES, O2, or other impurities are present.
Disobeys Markovnikov rule.
Product: terminal alkyl halides.
Hydroboration
Diborane (B2H6) adds readily to double bonds.
- Boron atoms is the Lewis Acd and attaches to less sterically hindered C atom.
- Oxidation-hydrolysis with PEROXIDE/Aq. base produces alcohol with ANTI-markovnikov, syn orientation.
Product: Alcohol with anti-Markovnikov.
Potassium Permangate (KMnO4)
Involved in Oxidation.
- Cold, dilute KMnO4 produces 1, 2 diols (vicinal) with syn orientation.
- Hot, basic KMnO4 plus acid produces:
- Nonterminal alkenes = 2M COOH
- Terminal - 1M COOH and 1 CO2 (if disubsituted it makes a ketone).
Ozonolysis
Involved in Oxidation.
Treatment of alkenes with OZONE, followed by reduction with Zn/H20 results in CLEAVAGE of double bond.
Product: Aldehyde.
If reduced with NaBH4 instead of Zn/H2) will result in Alcohols.
Peroxycarboxylic Acids
Alkenes can be oxidized with peroxycarboxylic acids.
e.g. Peroxyacetic acid (CH3CO3H) OR m-chloroperoxybenzoic acid (mcpba).
Products = Epoxides or Oxiranes.
Polymerization
Creation of long, MW chains composed of repeating subunits in alkenes.
Occurs through radical mechanism, requires HIGH TEMP and PRESSURE.
Synthesis of Alkynes
- Elimination of HX from geminal and vicinal dihalides with HEAT and BASE.
- Add existing Triple bond to Nucleophile by removing acidic proton with STRONG BASE.
Reduction of Alkynes
Can be hydrogenated with a catalyst.
Two Ways:
1. Lindlar’s catalyst (H2, Pd/BaSO4, Quinoline)
Product: Alkane (cis)
- Na, NH3 (liquid) -33 degrees C.
Product: Trans alkene.
Electrophilic addition of alkynes.
Electrophilic addition to alkynes occurs in same manner as it does alkenes. (X2 added)
Occurs according to Markovnikov.
Can be stopped at alkene or proceed further.
Product: Dihalo alkene or alkane
Free Radical Addition of Alkynes
Radicals add to triple bonds as with double bonds with ANTI-markovnikov (X-).
Product: trans isomer.
Because intermediate vinyl radical can isomerize to its more stable form.
Hydroboration Addition of Alkynes
Addition to triple bonds is same as double bonds.
Addition is syn and BORON adds first.
Boron can be replaced with proton from acetic acid = cis alkene.
Product: syn alkene.
Oxidation Addition
Alkynes can be oxidatively cleaved with either basic KMnO4 followed by acidification or Ozone.
KMnO4 Product: 2 M COOH
Ozone Product: 2 M COOH
Huckel’s Rule
4n + 2 pi electrons
Important indicator of aromaticity.
n = any nonnegative integer; thus can be 2, 6, 10, 14, 18, etc.
Aromatic Compounds
Aryl compounds or arenes (Ar)
1,2 substituted = Ortho- or 0-
1,3 subst = meta or m-
1,4 subst = para or p-
Physical properties are similar to hydrocarbons.
All 6C atoms are sp2 hybridized.
has delocalized pi electron system.
Electrophilic Aromatic Substitution
Most important reaction of aromatic compounds.
Reaction: electrophile replaces a proton on ring, producing substituted aromatic compound.
Common e.g.:
- Halogenation
- Sulfonation
- Nitration
- Acylation
Halogenation of Aromatic Compounds
An electrophilic aromatic substitution
Aromatic ring reacts with Br2 or Cl2 in presence of FeCl3, FeBr3, or AlCl3 to produce a monosubstituted product.
Product: aromatic ring with X.
Aromatic Rings \+ Br2 or Cl2 \+ FeBr3, FeCl3, or AlCl3
(name product)
Electrophilic Aromatic Substitution of Br or Cl to aromatic ring.
Sulfonation of Aromatics
An electrophilic aromatic substitution.
Aromatic reacts with fuming H2SO4 (mixture of SO3 and H2SO4) to form sulfonic acids.
Aromatic Rings + Fuming H2SO4 (SO3/H2SO4)
name product
An electrophilic aromatic substitution.
Formation of Sulfonic acids.
Aromatic ring + SO3H
Nitration of Aromatic Rings
An electrophilic substitution.
Mixture of nitric and sulfuric acids is used to create the nitronium ion, NO2+ (strong electrophile).
This reacts with Ar. rings to produce nitro compounds.
Aromatic Rings
+
Nitric (HNO3)/Sulfuric acids
(name product)
Product: Nitro Compounds
Friedel-Crafts Acylation
A carbocation electrophile, usually an acyl group is incorporated into Aromatic.
Usually catalyzed by Lewis Acids such as AlCl3.
Product = Ar-Acyl group
CH3C(=O)Cl + Aromatic + AlCl3 –> ?
Product: Aromatic Ring-Acyl group + HCl
Substituent Effects
- Activating, ORTHO/PARA-directing substituents: (electron donating) NH2, NR2, OH, NHCOR, OR, OCOR, R
- Deactivating, ORTHO/PARA-directing subs (weakly electron withdrawing): F, Cl, Br, I
- Deactivating, META-directing substituents (electron withdrawing): NO2, SO3H, Carbonyl compounds (COOH, COOR, COR, CHO)
NO2, SO3H, Carbonyl compounds (COOH, COOR, COR, CHO)
Deactivating, META-directing substituents (electron withdrawing)
Catalytic Reduction of Aromatics
Benzene rings can be reduced under vigourous conditions (elevated Temperature and Pressure) to yield cyclohexane.
Ruthenium and Rhodium are most common catalysts.
Product: cyclohexane
Aromatic ring + H2/Rh/C and high T/P –> ?
Benzene –> cyclohexane
Br2, Hv
electrophilic addition
occurs according to Markovnikov most substituted””
1) CH3MgBr
2) H3O+
Converts carbonyl compounds to alcohol
Addition reaction by Markovnikov.
1) NaBH4
2) H3O+
A reducing agent.
It is more selective and easier to handle, but will NOT reduce carboxylic acids and esters.
Will reduce aldehydes and ketones.
1) Lithium Aluminum Hydride
(LiAlH4 or LAH)
2) H3O+
A reducing agent.
Strong and powerful.
More difficult to work with.
Will reduce all aldehydes, ketones, carboxylic acids, and esters.
1) BH3
2) H2O2, OH-
Hydroboration
BH3 adds readily to double bonds.
Second step is oxidation-hydrolysis in an ANTI-markovnikov, syn orientation.
In presence of peroxides will convert to alcohol.
Cold, dilute KMnO4
An oxidizing agent.
Produces 1,2 diols (vicinal diols). a.k.a. glycols with syn orientation.
Alkene + Br2/CCL4 –> ?
Addition of halogens to double bonds is rapid.
Double bond is nucleophile and attacks X2.
Addition is anti, because X- attacks cyclic halonium ion in SN2 displacement.
AlCl3 + X2 or acyl group –?
AlCl3 is a lewis acid.
X2 in presence of lewis acid (FeCl3, FeBr3, AlCl3) produces monosubstituted products in good yield.
AlCl3 + acyl groups = Friedel-Crafts Acylation. will incorporate acyl group.
Zwitterion
An ion with both a positive and negative charge.
Alcohol + Carboxylic acid –> ?
Makes an ester
Henderson-Hasselbalch Equation
pH = pKa - log ([conjugate base]/[conjugate acid])
Nonpolar Amino Acids
Valine, Alanine, Isoleucine, Leucine, Proline, Phenylalanine, Glycine, and Tryptophan.
non - TV PIG PAL”
Polar Amino Acids
Methionine, Serine, Threonine, Cysteine, Tyrosine, Asparagine, and Glutamine.
Have polar, uncharged R-groups that are HYDROPHILIC, increasing the solubility of the amino acid in water.
Usually found on protein surfaces.
Acidic Amino Acids
Aspartic Acid, Glutamic Acid
R-group contains carboxyl groups. They have net negative charge at physiological pH and exist in salt form in the body. Play important role in substrate-binding sites of enzymes.
Have three distinct pKa’s
Basic Amino Acids
Arginine, Lysine, Histidine
Amino acids whose R-group contains an amino group and carry a net positive charge at physiological pH.
pH vs pI
If pH < pI, think positive charge.
If pH > pI think negative charge.
Peptide bonds
Link amino acid subunits between the carboxyl group of one amino acid and the amino group of another.
Formed via condensation reaction (water is lost).
Primary Structure
Refers to sequence of amino acids listed from N- to C- terminus, linked by COVALENT bonds btw neighboring chains.
Secondary Structure
Local structure of neighboring amino acids, governed mostly by HYDROGEN bond interactions.
Most common types are alpha-helix and beta-pleated sheet.
Alpha-Helix
Rod-like structure in which the peptide chain coils clockwise about a central axis.
e.g. keratin