O Chem General Flashcards
1 degree carbon
Primary carbon, attached to 1 other carbon
2 degree carbon
Secondary carbon, attached to 2 other carbons
3 degree carbon
Tertiary carbon, attached to 3 other carbons
4 degree carbon
Quaternary carbon, attached to 4 other carbons
Molecules with same formula and different connectivity, different properties
Constitutional isomers
Conformational isomers
Same molecule, different bond rotation (ex. Staggered vs eclipsed)
electrophile
likes electron density
- deprotonating
- (acid)
nucleophile
electron donor
- source of electron density
- proton-acceptor
- (base)
relative pKa values
A STRONG ACID has a low pKa; very likely to donate an H+ (and accept electron density)
A STRONG BASE has a high pKa; very likely to accept an H+ (and donate electron density)
pKa value of a STRONG ACID is generally…
pKa less than zero (a negative number).
The smaller the number, the stronger the acid.
pKa value of a STRONG BASE is generally…
pKa of 15 or larger.
We say the conjugate base is a strong base at these values.
The larger the number, the stronger the base.
EWG
Electron Withdrawing Group
Delocalizes electron density, which makes a weaker base, less able to accept a proton.
Stabilizes anions.
EDG
Electron Donating Group
Adds electron density and makes a stronger base better able to accept a proton.
Stabilizes cations.
E nomenclature
E (Entgegan) = apart, meaning of 4 groups attached to a double bond, the highest priority molecular groups are apart from each other.
Like in a “trans” shape, but E applies to groups that are different, and trans applies to identical groups.
Z nomenclature
Z (zusammen) = together, meaning of the four groups attached to a double bond, the 2 highest priority molecular groups are on the same side.
Like in a “cis” shape, but Z applies to groups that are different, and cis applies to identical groups.
Naming High Priority groups (via Cahn-Prelog System)
CIP
2) (tiebreaker) Use the next attached atoms until the FIRST point of difference.
#1) Highest atomic number = highest priority. (If atomic number the same, use atomic mass)
hyperconjugation
the donation of electron density from a sigma orbital to an empty orbital (often sigma * or p orbital).
(remember that the number of orbitals in = number of orbitals out, so lots of empty orbitals around.)
why is a tertiary carbon more stable than a primary or secondary?
3 degree carbon more stable because of potential for better distributed positive charge via hyperconjugation (where a filled orbital is donating electron density into an empty orbital).
Markovnikov’s Rule (regioselectivity)
observed that in HX additions, the X atom attaches to the highest degree carbon (3 >2>1)
Hammond’s Posulate
The structure and energy of the transition state can be approximated by the nearby high-energy intermediate.
The transition state is controlling the reaction pathway, but the intermediate can be studied more easily.
dipole
partial charge –concentration of negative charge separated from concentration of positive charge.
Le Chatelier’s Principle
When a shift in equilibrium occurs in a thermodynamically controlled reaction, the reaction will respond in a way that shifts back to equilibrium.
isomer
(same parts)
same formula, different construction
enantiomers
isomers that are non-superimposable mirror-images of each other
(described as “chiral”)
Very difficult to isolate because the energy barrier to convert between them is very low; they readily form a racemic mixture in an achiral environment.
stereoisomers
Same connectivity/bonding, differ in 3-D arrangement of atoms (sub-categories include enantiomers, geometric isomers)
chiral center
tetrahedral sp3 hybridized carbon that has 4 different groups attached
constitutional (structural) isomers
Same formula; differ in connectivity of atoms
Geometric Isomers
different arrangement in space around a non-rotating bond
meth-
1 C chain
eth-
2 C chain
prop-
3 C chain
but-
4 C chain
carbonyl compound or group
a functional group that contains a C double bonded to an O
Acid / base effects on reactions
Element — atomic size and bond length Charge (formal charge) Hybridization (resonance) Pi conjugation Element — charge delocalization via induction
anti vs. syn addition
Syn is the addition of two substitutes to the same side of the molecule; anti is the addition of two substitutes to the opposite side of the molecule.
Three categories of solvents
A solvent can be…
1) protic or aprotic
2) polar or apolar
3) an electron donor or nondonor
Why does “like dissolve like”?
When attractions between molecules in pure liquids are similar to attractions between the solute and solvent, then the free energy of mixing will dominate the solution will form.
Protic solvent
Consists of molecules that can act as hydrogen bond donors.
Vs aprotic
Polar solvent
Solvent that is not only is a polar molecule (meaning it has a significant dipole moment), but also has a high dielectric constant (assigned value based high interaction energy between ions).
Vs. apolar solvent
Electron donor solvent
Molecules containing O or N that can donate an electron lone pair.
Ex. Ether, THF, and methanol.
Vs. nondonor solvent
Bromine
Neutral, radical, element on the periodic table
Bromide
Anion, nucleophile
[ ]
Brackets around molecules indicates…
[ ] brackets indicate a state of fleeting existence in a reaction– an intermediate or a transition state.
Degrees of unsaturation
A calculation of how many carbons in an organic molecule have 4 separate bonds.
- For simple visual assessment– count rings and double bonds, subtract from full saturation potential.
- Simplified formula for C and H -only containing molecules: ((#C x 2 + 2) - #H) / 2
Abbreviation of a benzene ring
Ph
6 C ring with 3 double bonds
Racemic Mixtures
Chiral molecules racemize in a chiral environment, meaning they readily interconvert between their R and S stereoisomers. Both racemic mixtures and achiral molecules are optically inactive.
ex. Amine inversion–N readily interconverts between R and S stereoisomers, even if it requires tunneling.
Require a chiral starting material or a catylst to be optically active.
Naked cation
A cation (ion with + charge) that is unsolvated in solution
Naked anion
An anion (ion with - charge) that is unsolvated in solution
In an X2 addition reaction with H2O, why does the H2O serve as the nucleophile?
H2O outcompetes the X anion as nucleophile because
- It is in excess
- H2O helps form the intermediate by solvating the ions, lowering the energy and stabilizing the charge
- X anion is in a solvent cage of H2O, lowering its reactivity as a nucleophile
What makes 3-member rings so unstable?
- Ring strain. Highly strained bond angles (60 vs. 109.5 ideal); bonds actually bend causing misaligned orbitals. Compromise between bond alignment and bond angle.
- No potential for electron density donations between filled and unfilled orbitals via hyperconjugation.
These factors raise the energy and make these rings very unstable.
Why is cyclohexane chair configuration so stable?
- No eclipsing interactions.
- All sigma and sigma * orbitals can overlap and engage in hyperconjugation.
- Close to 109.5 degree bond angles.
Geometry of bridgehead Carbons
A carbon that is at a bridgehead of a multiring molecule must be tetrahedral and sp3 hybridized. No double bonds. Anything other than tetrahedral would cause too much strain, raising energy and destabilizing the molecule.
(Bredt’s Rule)
A value
A value is documented energy cost for a substituent to be axial vs. equatorial on a cyclohexane ring.
Measured in kcal/mol.
Higher value = more steric bulk.
A value of a methane group -CH3
-CH3 has an A value of 1.74 kcal/mol
General energy difference for axial vs. equatorial position of substituents on ring
Molecule will have lower energy and be more stable when the substituents with greater A value (steric bulk) are in the equatorial positions.
Equatorial positioning gives fewer steric interactions and has lower energy, making molecule more stable; it gives anti interaction.
Axial positioning gives gauche interaction, higher energy and less stable than equatorial position.
All about chair flips
- Depict the same 6-member ring in two different configurations. (Other less stable configurations include half chair and twist-boat).
- Use EQM arrows when drawing.
- 6 member ring drawn with 3 pairs of parallel bonds.
- Axial substituent bonds are vertical.
- Equatorial substituent bones are parallel to the nonadjacent ring C-C bonds.
- Each C tetrahedral.
- Up axials go on up C, down axials on down C.
equatorial
parallel lines
role of a catalyst
lowers the energy of activation to speed up a reaction
What stabilizes a carbo cation?
- filled sigma bond orbitals donating electron density into the C empty P orbital via hyperconjugation
- Delocalization of positive charge character via Pi conjugation, if adjacent to a pi system
- ???Nearby EDG, if present, via induction????
Lindlar’s Catalyst
Lindlar’s catalyst is also referred to as quinoline, or PD, CaCO3.
Used with H2 reaction to reduce an alkyne to an alkene. Stops there–not strong enough to reduce further to alkane.
Meso compond
molecule that has an R and an S stereocenter, but no enantiomer. The internal symetry is such that there is an internal mirror plane and just one molecule (no stereoisomer).
Why don’t we see flat, planar cyclohexane?
- would make 120 degree bond angles; too big for cp3 hybridization; causes strain on the bond angles outside the ring
- lots of eclipsing ineractions
Reactivity of alcohols vs. thiols
(O vs S)
The S-containing thiols form longer, very p-rich, weaker bonds with H (than oxygen counterparts).
S-H bonds more reactive than O-H counterparts.
Likewise, S makes a weaker base than O.
Protic Solvents
Protic solvents are capable of Hydrogen-bonding.
(vs. aprotic can not participate in H bonding)
Will have a H directly connected to a highly electronegative atom, giving the H atom positive charge character.
Stabilizing for anions (neg -). The molecules align based on charge attraction, and electron density on the anion donates into the sigma * orbital of the H-X bond. This lowers the energy of the system, stabilizing the molecules.
Solvated X anion less reactive as a nucleophile and as a base.
Electron-Donating Solvents
Will have a lone pair present; electron-rich. Stabilize pos charge cations (but leave anions naked)
Good if you want a naked anion that can still serve as a nucleophile.
Polar Solvents
- Ability of a solvent to shield ions from each other
- Stabilizing for polar molecules
- Dielectric constant measures strength of intermolecular forces as a BULK solvent
(vs. dipole moment measures polarity of an individual molecule)
Tautomers
Tautomers are constitutional isomers that readily interconvert.
Enol tautomerization
When you get an ENOL (C-O single bond adjacent to a C=C double bond) O will protonate the C and take electron density to make its own O=C double bond.
Enol
An enol is a C-O single bond adjacent to a C=C double bond; generally unstable and readily convert
Kinetically-controlled reaction
the energy difference of transition states control the reaction outcome
Rate
Thermodynamically-controlled reaction
the stability of the reactants and products determine the outcome
Favorability
Boron bonding
B can readily convert between 3 or 4 bond attachments
Definition of a Substrate
The chemical of interest in a reaction, the chemical that is reacting with the reactants and being modified
Main polar protic solvents
Fancy waters
Amides (N bonded to H for H-bonding)
