Organic Chemistry Flashcards
Highest-Priority Functional Group
the most oxidized carbon
Diols / Glycols
Alcohols with two hydroxyl groups
indicated by the suffix -diol
Diols with hydroxyl groups on the same carbon
Germinal Diols
aka hydrates
Diols with hydroxyl groups on adjacent carbons
Vicinal Diols
Aldehydes are named by replacing the -e of the parent alkane with …
-al
chain terminating carbonyl
What are the common names of the aldehydes methanal, ethanal, and propanal?
formaldehyde, acetaldehyde, and propionaldehyde
Ketones are named by replacing the -e of the parent alkane with …
-one
What is the most oxidized functional group that applies on the MCAT?
Carboxylic Acid
Carboxylic acids are named by replacing the -e of the parent alkane with …
-oic acid
Describe an ester.
Carboxylic acid derivative where the hydroxyl group is replaced with an alkoxy group (-OR; R= hydrocarbon chain)
Esters are named by replacing the -oic acid of the parent carboxylic acid with …
-oate
Describe an amide.
Carboxylic acid derivative where the hydroxyl group is replaced by an amino group (nitrogen-containing group).
Esters are named by replacing the -oic acid of the parent carboxylic acid with …
-amide
any substituents attached to the amino group are labeled with a capital N-
Describe an anhydride.
A dehydration reaction between two carboxylic acids
usually a cyclic molecule
The common names for the aldehydes and carboxylic acids that contain two carbons start with the prefix …
Acet-
What is the least similar of all the isomers?
Structural (Constitutional) Isomers
same formula but different connections
different chemical and physical properties
Stereoisomers
same atomic connectivity but different arrangement in space
conformational isomer: differ in rotation around a single sigma bond
configurational isomer: interconverted only by breaking a bond
Ring strain on cycloalkanes
Angle strain – bonded angles deviate from their ideal values
Torsional strain – cyclic molecules assume conformations that are eclipsed or gauche
Nonbonded strain (van der Waals repulsion) – nonadjacent atoms competing for the same space (steric hinderance in the flagpole interactions of the cyclohexane boat conformation)
Cyclohexane in a chair conformation
Hydrogen atoms perpendicular and parallel to the place of the ring called what, respectively?
perpendicular (up and down) = axial
parallel (sticking out) = equatorial
What are the two categories of configurational isomers?
Enantiomers and Diastereomers
both are optical isomers because the spatial arrangement of groups affects the rotation of plane-polarized light
Enantiomers
same connectivity but opposite configuration at EVERY chiral center in the molecule
nearly identical chemical and physical properties
Optical activity of enantiomers
rotates plane to the right (CW) = dextrorotary (+)
rotates plane to the left (CCW) = levorotary (-)
Optical activity in a racemic mixture of enantiomers?
(+) and (-) enantiomers present in equal concentrations
optical rotation cancels itself out so there is NO ROTATION OF PLANE-POLARIZED LIGHT
Diasteromers
occur when a molecule has two or some stereogenic centers and differs at some, but not all, of these centers
DIFFERENT CHEMICAL AND PHYSICAL PROPERTIES
A molecule has n chiral centers. How many possible stereoisomers are there?
2^n
Optical activity of enantiomers vs diastereomers
knowing the specific rotation of one diastereomer gives NO INDICATION on the specific rotation of another diastereomer
enantiomers ALWAYS have equal and opposite rotations
Meso Compound
a molecule with chiral centers BUT possesses an internal plane of symmetry
NO optical activity
(E) and (Z) forms of isomers
used for polyunsaturated double bonds
related from then highest priority substituent (highest atomic number) on each double bonded carbon
Z = SAME SIDE
E = OPPOSITE SIDE
Wedges vs dashes in Fischer projections
Wedges = project OUT from the plane of the page
Dashes = bonds going INTO the plane of the page
A molecular orbital is formed by a head-to-head or tail-to-tail overlap. What is the resulting bond?
sigma bond
all SINGLE BONDS are sigma bonds, accommodating two electrons
When two p-orbitals line up in a parallel fashion, their electron clouds overlap. What is the bonding molecular orbital called?
a pi bond
a pi bond on top an existing sigma bond is a DOUBLE BOND (two pi bonds for a triple bond)
NOTE: pi bonds cannot exist independently of a sigma bond; only when the sigma bond is formed do the p-orbitals of adjacent carbon become parallel and form the bond
Which is stronger, a sigma bond or a pi bond?
SIGMA BOND IS STRONGER
An element such as carbon has four equivalent sigma bonds. How is this possible since the valence electrons live in different subshells / orbitals?
Hybridization of the orbitals
Carbon actually has a stable 2sp^3 hybridized ground state
How do you predict H-NMR splitting patterns?
the n+1 rule
n = number of nonequivalent neighboring hydrogens
Oxidizing agents vs reducing agents.
Oxidizing agents: THEY THEMSELVES are reduced by oxidizing another agent
Reducing agents: THEY THEMSELVES are oxidized by reducing another agent
A Lewis acid is a what? What about a Lewis base?
Lewis Acid – electron acceptor in the formation of a covalent bond; vacant p-orbital; electrophiles
Lewis Base – electron donor in the formation of a covalent bond; lone pair of electrons; nucleophiles
Coordinate Covalent Bond
covalent bonds in which both electrons in the bond came from the same starting atom (the Lewis base)
comes from the interaction of Lewis acids and bases
Bronsted-Lowry acid? Bronsted-Lowry base?
acid – can donate a proton
base – can accept a proton
if the molecule can act as both a Bronsted-Lowry acid and base, it is AMPHOTERIC
The acid dissociation constant and pKa?
Ka = measures the strength of an acid in solution
Ka = [H+][A-] / [HA]
NOTE: pKa = -log(Ka)
What is special to note about alpha-hydrogens and acidity of functional groups?
the enol form of carbonyl-containing carbanions is stabilized by resonance
thus, these alpha-hydrogens are acidic and easily lost
Acidity increases with….
periodic table trend
decreasing bond strength and increasing electronegativity
when the trends oppose each other, BOND STRENGTH takes precedence
Nucleophiles
“nucleus-loving” species with wither lone pairs or pi bonds that can form new bonds
What is the technical definition between nucleophilicity and basicity?
Nucleophilicity – relative rate of reaction with an electrophile (KINETIC PROPERTY)
Basicity – related to equilibrium position of a reaction (THERMODYNAMIC PROPERTY)
Effects of the following toward nucleophilicity:
Charge
Electronegativity
Steric Hindrance
Solvent
Charge – increases with increasing charge (negative charge)
Electronegativity – decreases with increasing electronegativity
Steric Hindrance – decreases with bulkier molecules
Solvent – protic solvents can decreases nucleophilicity by protonating the nucleophile or through hydrogen bonding
Halogen nucleophilicity in polar protic solvent?
i.e. carboxylic acids, ammonia, water
nucleophilicity increases DOWN the periodic table
I- > Br- > Cl- > F-
weak acids, such as HF interact with the protons in solution and are less able to access the electrophile
Leaving groups? When do they occur?
IF the electrophile DOESN’T have any empty orbitals, a good leaving group stability will increase the likelihood of a reaction
if empty orbitals are present, the nucleophile can bond without displacing the leaving group
Leaving groups? What is the reaction functionally the opposite of?
molecular fragments that retain the electrons after heterolysis
OPPOSITE to coordinate covalent bond, since both electrons are given to one of the two products (heterolytic reaction)
SN1 Reactions
Unimolar nucleophilic substitution reaction
1st Step (RATE LIMITING): The leaving group leaves, generating a positively-charged carbocation
2nd Step: Nucleophile attacks the carbocation
more substituted carbocation = more stable (alkyl groups stabilize the positive charge)
SN1 Reaction Kinetics
rate of reaction depends ONLY on concentration of alkyl group containing the leaving group (substrate)
anything that accelerates the formation of the carbocation will increase the rate of the reaction
SN1 Reaction KStereochemistry
reaction passes through a planar intermediate so it produces a RACEMIC MIXTURE
nucleophile can attack from either side
SN1 Reaction Stereochemistry
reaction passes through a planar intermediate so it produces a RACEMIC MIXTURE
nucleophile can attack from either side
SN2 Reactions
Bimolecular nucleophilic substitution reaction
ONLY STEP: nucleophile attacks the compound at the same time as the leaving group leaves (concerted reaction)
SN2 Reaction Kinetics
nucleophile displaces the leaving group in a backside attack
nucleophile must be STRONG and the substrate cannot be sterically hindered
less substituted carbon is more reactive
concentration of the nucleophile and substrate BOTH determine the rate
SN2 Reaction Stereochemistry
inversion of the relative configuration
if the nucleophile and leaving group have the same priority, this will result in a change in the absolute configuration (R) to (S) or vice-versa
Oxidation state definition
indicator of the hypothetical charge an atom would have if all bonds were completely ionic
How should you view oxidation and reduction in organic chemistry?
oxidation is increasing the number of bonds to oxygen or other heteroatoms (atoms other than carbon or hydrogen)
reduction is increasing the number of bonds to hydrogen
Oxidizing agent
ACCEPTS an electron from another species so it is itself REDUCED
good oxidizing agents have a high affinity for electrons or unusually high oxidation states
What do oxidizing agents often contain?
a metal bonded to a large number of oxygen atoms
What do reducing agents often contain?
metals bonded to a large number of hydrides
How are protecting groups typically removed?
an ACID WORKUP
How are diols typically used in a reaction?
PROTECTING GROUP for a ketone
Ortho, meta, para?
Ortho = groups on adjacent carbons
Meta = groups separated by one carbon
Para = groups are on opposite side of the ring
What reactant produces aldehydes out of alcohols?
PCC
pyridinium chlorochromate
What are aldehydes converted into with oxidizing agents?
germinal diols and then into carboxylic acids
Jones oxidation
primary alcohol oxidized to a carboxylic acid by chromium trioxide
need acidic conditions in aqueous solution
CrO3
What is a mesylate and tosylate?
react with hydroxyl group of alcohol to be a much better leaving group OR act as protecting groups for alcohols
mesylate is -SO3CH3 group
tosylate is -SO3C6H4CH3
Alcohol role as protecting groups?
aldehydes or ketones can be reacted with two equivalents of an alcohol or diol, forming acetals (primary carbon with two -OR groups) or ketals (secondary carbon with two -OR groups)
A phenol is oxidized to form a what? Then further oxidized to form?
phenol –> quinone –> hydroxyquinone
In the presence of water, aldehydes and ketones react to form …
germinal diols (1,1-diols)
An aldehyde or ketone is treated with one equivalent of an alcohol. The result is a …
What about two equivalents of an alcohol?
ONE = hemiacetal (basic conditions)
TWO = acetal (catalyzed under anhydrous acid conditions)
Imine
compound with a nitrogen atom double-bonded to a carbon atom
simplest case – ammonia adds to the atom and water is lost (nucleophilic substitution)
S hydrogen cyanide attacks a aldehyde or a ketone. The resulting product is called a …
cyanohydrin
HCN
The two most common hydride reducing agents on the MCAT are
lithium aluminum hydride and sodium borohydride
LiAlH4 and NABH4
Michael Addition reaction
carbanion attacks (made from alpha-hydrogen with strong base, LDA, KH, or OH) an alpha, beta-unsaturated carbonyl compound
Kinematic vs thermodynamic products. Which is formed and when?
I.e. enolate formation
Kinetic product – formed rapidly but less stable (double bond to the less substituted alpha-carbon); formed in reactions that are rapid, irreversible, lower temperature, with a strong, sterically hindered base
Thermodynamic product – formed slowly due to steric hinderance but is more stable (double bond to the more substituted alpha-carbon); formed in reactions that are high temperature, slow, reversible, and weaker, smaller bases
Amide formation from a carboxylic acid?
the nucleophile must be ammonia or another amine
What reduction agent is strong enough to reduce carboxylic acids to a primary alcohol?
Lithium aluminum hydride
LiAlH4
A chair conformation in which both substituents are both … will ALWAYS be more stable.
EQUATORIAL
NOT axial (more steric hinderance)
cic-trans isomers of a subcategory of what isomer?
Diastereomer
non-mirror image stereoisomers
Methylsulfonyl chloride?
a protecting group for ALCOHOLS; turns into mesylates
What is the normal sp3 bond angle?
109.5 deg
Transesterification
an alcohol acts as a nucleophile and displaces the esterifying group on an ester
Strecker Synthesis
forms an amino acid from an ALDEHYDE
RACEMIC MIXTURE; BOTH L- AND D-AMINO ACIDS FORMED
aldehyde, ammonium chloride (NH4Cl), and potassium cyanide (KCN)
ammonia attacks after oxygen is protonated and forms an imine; CN- anion attacks forming a nitrile group; final product at end of step one is an aminonitrile (contains -NH4 and -CN)
in final step, two equivalents of water knock off the protonated nitrile carbon
Characteristic wavenumber absorptions from IR spectrometry.
O-H: broad between 3300 and 3000 cm-1
N-H: sharp around 3300 cm-1
C=O: sharp 1700 cm-1
What is the biggest piece of information we obtain from ultraviolet (UV) spectrometry?
wavelength of maximum absorbance – the extent of conjugation
conjugation up, lower energy of transition, greater the wavelength of maximum absorbance
What does the magnitude of a H-NMR peak indicate?
the number of protons it contains
remember: equivalent hydrogens will resonate at the same frequency (same peak)
Explain H-NMR deshielding?
the attached atom has other electronegative species that pull electron density away from the proton
this exposes the hydrogen (deshields) from the magnetic field leading to a LEFTWARD/DOWNFIELD shift (higher delta; higher ppm)
How to determine spin-spin coupling (H-NMR)?
n+1 rule
if a proton has n protons that are on an adjacent atom (3 bonds away), it will be split into n+1 peaks
NOTE: DO NOT include protons attached to oxygen or nitrogen
What is the chemical shift (ppm) downfield of an aromatic ring?
6.0-8.5
How would we separate two products with similar boiling points?
fractional distillation
Why would you use vacuum distillation over simple distillation?
if the product has a very high boiling point
using vacuum decreases the temperature required to reach the required vapor pressure (keeps product from being degraded)
Retardation factor (Rf) equation from a TLC experiment
Rf = distance spot moved/distance solvent front moved
Decarboxylation occurs with which molecules?
beta-keto acids and beta-dicarboxylic acids
Sodium borohydride reduces carboxylic acids to …
TOO GENTILE to reduce carboxylic acids; NO CHANGE
How do anhydrides, especially cyclic anhydrides, form?
SPONTANEOUSLY from dicarboxylic acids with HEAT
IR spectroscopy is most useful for determining …
double and triple bonds
What is the chemical shift associated with an aldehydic proton?
9 to 10 ppm
Which isotopes are useless to use for NMR?
isotopes with no magnetic moment!
NOTE: nuclei with odd mass numbers or those with an even mass number but an odd atomic number will have a NONZERO magnetic moment
Before absorbing an ultraviolet photon, electrons can be found in …
the highest occupied molecular orbit (HOMO)
it is excited to the lowest unoccupied molecular orbit (LUMO)
IR spectrometry trend with higher order bonds?
higher-order bonds tend to have HIGHER absorption frequencies
note: conjugation and delocalization will shift the absorption frequency LOWER
Wavenumber (v) is directly proportional to?
Inversely proportional to?
Directly: FREQUENCY
Inversely: WAVELENGTH
Ina carboxylic acid, the absorption spectra for an -OH bond is shifted from 3300 cm-1 to about …
3000 cm-1
What solvent should be used for a gravity filtration?
WARM or HOT
we want the desired product to remain soluble to be retained in the filtrate
if too cold, the product can precipitate and remain in the filter (residue)
Hemiketal formation can be acid- or base-catalyzed. However, ketal formation MUST be …. catalyzed
has to be ACID catalyzed
acid protonates the hydroxyl oxygen to form a good leaving group (H2O)
the second alcohol then adds to the resonance stabilized carbocation
How does the membrane of a neuron show select permeability?
the K+ channels are more “leaky” because there are more of them on the membrane
so, the membrane shows a select permeability of K+ over Na+
