OChem Flashcards

Functional group
Terms Definitions
Alkene
...
isopropyl
--CH(CH3)CH3
Homolysis electron
One
ester stretch
1735cm⁻¹
E2 on sp2
Depends
butyl
molecular mass = 57
1 -OH------?-------> aldehyde
PCC/ CH2Cl2
C=C stretch
~1620-1680cm⁻¹
- variable intensity
SN2
mechanism that is stereospecific: inversion of stereochemistry
sp
triple bond in a molecule
Acetylene
Acetylene is a hydrocarbon belonging to the group of alkynes, considered to be the simplest of all alkynes as it consists of two hydrogen atoms and two carbon atoms.
E2
mechanism where the reaction rate depends on the strength of the incoming base and the leavability of the leaving group
tertiary amine---?----> quartenary amine
alkyl halide/ NaOHC
branching
decreases boiling point, melting point and density.
Oxidizing Agents
H2CrO4 (Aldehydes), Ag2O, O2 (Aldehydes, radical chain reaction), Powerful oxidants at high T and high acid or base concentration (e.g. HNO3) (Ketones)
DCC coupling
1. DCC (dicyclohexyl carbodiimide) converts the OH of the carboxylate grp in an AA into a good leaving grp
2. amino grp of a 2nd AA attacks the carbonyl carbon of the "activated" AA
3. DCC leaves w/the oxygen to which it is bonded
Nitroso
Nitroso refers to a functional group in organic chemistry which has the general formula RNO.
The higher the concentration
The faster the rate
Oxymercuration-Reduction: hydration #3
-Hydration without using acid
- Markovnikov addition, BUT...
- No possibility of carbocation rearrangement
- Downside: toxic reagent
- Dont worry about the mechanism
Oxidation
Addition of O or removal of Hs
Anhydride Reaction with H2O
Makes two component acids
Fischer Esterification
Carboxylic Acid + Alcohol -(H2SO4)-> Ester + H2O (Equilibrium Reaction)
subunit
a single polypeptide chain that is part of a large complex containing many subunits (a multisubunit complex)
Carbonate ester
A carbonate ester is a functional group in organic chemistry consisting of a carbonyl group flanked by two alkoxy groups.
Boiling points depends on ____,____,____
IMFS; Comparative BP's (alkans<ethers<amins<alcohols)
Halogenation Mechanism
Halogens add to pi bonds because halogens are polarizable:
- C=C induces a dipole in X2: X+ - X -
- X is then attracted to the nucleophilic double bond
Proof that halogenation follows a different mechanism from that of hyrohalogenation or hydration:
- no carbocation rearrangements occur
- only anti addition of X2 is observed
- These facts suggest that carbocations are not intermediates.
E2 if halide on 3
Yes and Beta H
Aromatic Transition States
Found in: Decarboxylation of beta-keto acids and beta-dicarboxylic acids; Diels-Alder; Claisen Rearrangement; Cope Rearrangement
Epoxy Resins
Polymerization of a monomer with at least two epoxygroups
downfield
- more deshielded (L)
Ex. a set of protons near an electroneg.grp is said to be deshielded & will appear downfield (L)
Neils Bohr
Postulated E levels of e were quantizedwhen an atom gives off an electron it moves into a higher level
leaving group
atom or group of atoms which is electron withdrawing and has a tendency to be easily removed from a carbon structure
Alcohols - Structure and Bonding
Alcohols:
-contain a hydroxy group (OH) bonded to an sp3 hybridized carbon
-classified according to the number of alkyl groups attached to carbon bearing the OH:
RCH2OH = 1
R2CHOH = 2
R3COH = 3
Alkene-----?------ adds -OH and H marks rule
1. Hg(OAc)2/ 2. NaBH4
Alcohols (Mass Spec)
Commonly lose H2O, giving strong M-18 peak (and almost no M peak); can also lose an alkyl group from R-CR'2-OH to give R-radical and resonance stabilized CR'2=OH+
common oxidizing agents (able to absorb e⁻ & be reduced)
Chromic Acid (H₂CrO₄)
Chromate Salts (CrO₄²⁻)
Dichromate Salts (Cr₂O₇²⁻)
Permanganate (MnO₄⁻)
Chromium Trioxide (CrO₃)
Pyridinium Chlorochromate (PCC)
E1 mechanism
E1 is a model to explain a particular type of chemical elimination reaction in which there is a two-step process of elimination ionization and deprotonation.
Effect of Leaving Group
A better leaving group increases the rate of both Sn1 and Sn2 reactions
Preparation of Alkenes: Refresher
Alkenes can be prepared from alkyl halides, tosylates, and alcohols via elimination reactions.
The most stable alkene is usually formed as the major product.
Chain Transfer Reaction
Radical changes places with H to give more stable radical, which results in branching
Sn2 rate speed R
The more r groups, the slower the reaction
Comparing E1 & E2 Reactions: Stereoselectivity
E2 Stereoslectivity:
-if C from which H is removed is bonded to 2 H, get mostly E some Z
-if C from which H is removed is bonded to 1 H, get mostly anti elimination (can be mostly E or mostly Z)
E1 Steroselectivity:
-Get mostly E
Mechanism of Ether Cleavage
The mechanism of ether cleavage is Sn1 or Sn2, depending on the identity of R.
When 2 or 3 alkyl groups are bonded to the ether oxygen, the C-O bond is cleaved by an Sn1 mechanism involving a carbocation.
With methyl or 1 R groups, the C-O bond is cleaved by an Sn2 mechanism.
Carboxylic Acid Derivative Reaction with Gilman
Acid Chloride (and no others) ---(1. R2CuLi, Ether, 78oC, 2. H2O)---> Ketone
Racemization in Sn1 reactions
Step 1: loss of the leaving group in generates a planar carbocation (achiral)
Step 2: Attack by :Nu can occur on either side to afford two products, which are a pair of enantiomers.
Because there is no preference for nucleophilic attack from either direction, an equal amount of the two enantiomers is formed - a racemic mixture (process is called racemization)
hydrogenation of π bonds of alkynes
- H₂ (w/2 equivalents)
- complete reduction
- uses Ni, Pd, or Pt
Syn and Anti Addition to Alkenes
Because the carbon atoms of a double bond are both trigonal planar, the elements of X and Y can be added to them from the same side or from opposite sides:
- syn addition: both X and Y are added from the same side
- anti addition: X and Y are added from opposite sides
Comparison of E1 and E2 Mechanisms
The strength of the base is the most important factor in determining the mechanism for elimination.
E2:
-much more common and useful
-favored by strong, negatively charged bases, especially -OH and -OR
-The reaction occurs with 1, 2, and 3 alkyl halides.
E1:
-much less useful because a mixture of Sn1 and E1 products usually results
-favored by weaker, neutral bases, such as h2o and ROH
Rate
K[reactants]
Propane
CH3CH2CH3
Sn1 degree
3
High temperature range
80-100
ethyl
molecular mass = 29
2 -OH----?------> Ketones
PCC/ CH2Cl2
O−H stretch
~3200-3650cm⁻¹
- broad, strong
E1 if halide on 1
No
Hemiacital Names
5-membered: -pyran- 6-membered: -furan-
Racemization
In chemistry racemization refers to partial conversion of one enantiomer into another, which often occurs in SN1 substitution.
SN1
polar protic solvents (SN1 or SN2)
secondary amine---?----> tertiary amine
allkyl halide/ NaOH
Distillation
Technique used to separate two miscible liquids
Isotactic Polymer
Identical configurations at each stereocenter
C=O stretch
~1680-1735cm⁻¹
- always look for this 1st
- very strong & very intense
Electrophilic addition
An electrophilic addition reaction is an addition reaction where, in a chemical compound, a pi bond is removed by the creation of two new covalent bonds.
Ozonolysis
Ozonolysis is the cleavage of an alkene or alkyne with ozone to form compounds in which the multiple carbon-carbon bond has been replaced by a double bond to oxygen.
Polar aprotic solvents
No OH or NH bonds
Degree of Unsaturation
Unsaturated hydrocarbons: have fewer than the maximum number of hydrogen atoms per carbon (2n+2) (alkenes, alkynes)
Each pi bond or ring removes two hydrogen atoms from a molecule, and this introduces one degree of unsaturation.
Degree of unsaturation: the number of pi bonds and cyclic strctures in a molecule (remember: a oduble bond has on pi bond, a triple bond has two pi bonds)
General formula for hydrocarbon: CnH2n+2-2x where x is the degree of unsaturation in the molecule
Precipitation
Occurs when a crystallizing mixture is cooled too quickly
Amide Reduction
Amide --(1. LiAlH4, 2. H2O)--> Amine
Claisen Rearrangement
Thermal rearrangement of allyl phenyl ethers to 2-allylphenols (oxygen is a member of the rearrangement ring)
carboxylic acids
- relatively strong WEAK acids
- c.acids form strong hydrogen bonds bc the carboxylate grp contains both a H-bond donor & a H-bond acceptor
- c.acids that have carbonyl grps β to the carboxylate are unstable
Thiol
A thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom. Often referred to as mercaptans, these compounds are the sulfur analogues of alcohols.
Aufbau Principle
An electron goes into the atomic orbital with the lowest energy first
Markovnikov's Rule
With an unsymmetrical alkene, HX can add to the double bond to give two constitutional isomers, but only one is actually formed.
Markovnikov's rule:
- the electrophile (often H) adds to the sp2 carbon that is bonded to the greater number of hydrogens.
- in the addition of HX to an unsymmetrical alkene, the H atom adds to the less substituted carbon atom - that is, the carbon that has the greater number of H atoms to begin with
- "them that has, gets"
- results in formation of the most stable carbocation.
E2 if halide on 2
Yes and beta H
Cyclic Structure of Monosaccharides
Monosaccharides almost entirely exist as five and six membered hemiacetals
ALL animal AA:
are derived from L-glyceraldehyde, & are thus all L-configuration
δ+/δ-
Partial plus (< full +1 ion charge) or partial minus (< full -1 electron charge) dipole charge
Substitution bonds
One sigma bond breaks and another one forms
Reactivity of Hydrogen Halides
-The reactivity of hydrogen halides increases with increasing acidity.
-Cl- is so poor a nucleophile that an additional lewix acid catalyst (ZnCl2) is needed with 1 ROH.
-Complexation of ZnCl2 with the O of ROH makes a very good leaving group that facilitates the Sn2 reaction.
Bumping
A violent surge which can occur when a liquid is heated without boiling stones
Carboxylic Acids (Mass Spec)
Alpha-cleavage to give COOH+ (m/z=45); Also, McLafferty Rearrangement
markovnikov additions
(4 things)
1. adds substituant to the most substituted C available
2. rearrangements possible
3. major/minor products
4. two steps
Syn and Anti addition
Syn and anti addition are different ways in which two substituents can be added to a double bond or triple bond.
Predicting the Mechanism of Nucleophillic Substitution Reactions
Four factors are relevant in predicting whether a given reaction is likely to proceed by an Sn1 or an Sn2 mechanism:
-The alkyl halide - CH3X, RCH2X, R2CHX, R3CX
-The nucleophillic - strong or weak
-The leaving group - good or poor
-The solvent - protic or aprotic
Halogenation: Electrophilic Addition of Halogen
Halogenation: addition of X2 (X=Cl or Br) to an alkene to form a vicinal dihalide.
Reduction of COOH
Only LiAlH4, which takes it to 1o alcohol
Pka trend of good leaving groups
Low pka values because strong conjugate acids
Substitution and Elimination Reactions of Alcohols
-Treatment of alcohols with a strong acid protonates the O converting the bad leaving group -OH into h2o, a good leaving group.
This makes it possible to perform substitution and elimination reactions on alcohols.
1 -OH-----?------> carboxylic acid
CrO3/ H3O, actone or KMnO4, OH/ H2O, heat
Acid Chloride Reaction with H2O
R-COCl + H2O --> R-COOH + HCl
Substrate Reactivity in Sn1 reactions
Sn1 reaction rate is affected by the type of alkyl halide involved: As the number of R groups on the carbon with the leaving group increases, the rate of an Sn1 reaction increases.
(Sn2 Factor = stereo factor) (Sn1 Factor = carbocation stability)
unsaturated fatty acids
- fatty acids have 1 or more doubB in the tail
- almost always Z (cis)
In words, what Does adding POCl3/ pyridine to a 2 -OH do?
It dehyrdates the alcohol and creates a double bond
Reactions of Ethers with Strong Acid
When ethers react with HBr or HI, both C-O bonds are cleaved and two alkyl halides are formed as products.
Ethers are unreactive with everything except HX, so ethers are commonly used as solvents:
-diethyl ether, tetrahydrofuran, tetrahydropyran, 1,4 dioxane, 1,2-dimethoxyethane, tert-butyl methyl ether
Sn2 degree
1
Sn2 on sp2
No
methyl
molecular mass = 15
ether------?-----> alcohol + alkene
CF3CO2H
disaccharide
2 monosaccharides bonded together
Sn2 if halide on 1
Yes
Grignard Reagents with a,b-Unsaturated Carbonyl
1,2-addition
Alkyne
Traditionally known as acetylenes or the acetylene series, the alkynes are hydrocarbons that have at least one triple bond between two carbon atoms.
ethanol<40%water60%ethanol<80%water20%ethanol<water
relative reactivity of solvents (water and ethanol for SN1 reactions)
primany amine----?-----> secondary amine
alkyl halide/ NaOH
Holdup
Condition where liquid collects on glassware and reduces the amount of liquid distilled
1,2 vs. 1,4
1,2 Kinetic 1,4 Thermodynamic
C≡C stretch
~2100-2300cm⁻¹
- look for this 2nd
- variable intensity
Aldehyde
An aldehyde is an organic compound containing a terminal carbonyl group.
Hydroboration-oxidation reaction
Employing borane in tetrahydrofuran in the first step, the hydroboration-oxidation reaction is a two-step organic chemical reaction that converts an alkene into a neutral alcohol by the net addition of water across the double bond.
Conjugate base is stuff (with or without) added proton
without
Emulsion
Suspension of one material in another that does not separate quickly by gravity
Enolate Anion
Ketone or Aldehyde loses an alpha-hydrogen (to a base), giving a resonance stabilized anion
alpha-Halogenation
Aldehydes and ketones with an alpha-H can react over acid or base with X2 to give alpha-Halo-...one
Linear
180°Two atoms bound to central atom, no lone pair
Acetyl
Acetyl (ethanoyl), is the term for a functional group which is the acyl of acetic acid.
Alcohol
An alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group
Hyperconjugation
when an electron in a sigma orbital can overlap with an anti-bonding orbital
Naming Alkynes
Alkyne nomenclature similar to that of alkenes.
In the IUPAC system, change the -ane ending of the parent alkane name to the suffix -yne.
Choose the longest continuous chain that contains both atoms of the triple bond and number the chain to give the triple bond the lower number.
Diyne: compound containing two triple bonds
Triyne: compound contatining three triple bonds
Enyne: compound containing both a double and triple bond
-number chain to give first unsaturation (C=C or CtripleC) the lower number
cis isomer
less stable, more energy and more polar
Thermoplastic
A polymer that can be melted and molded into a shape which it will retain when cooled
Benedict's test
- chemical assay that detects the carbonyl units of sugars
- distinguishes hemiacetals from acetals
- Benedict's reagent is used to oxidize a sugar's aldehyde ketone to the corresponding carboxylic acid, yielding a reddish precipitate
2s
N=2 and l=0Middle looks like 1s with a node and then a raise and fall in density
E on diagram
Determines the height of the energy barrier
Stereochemistry of Reaction of Alcohols with HX
As in other substitution reactions,
-Sn2 reactions give inverted
-Sn1 reactions give raceimization
Retention Factor
How far a compound travels on TLC relative to the solvent
Diels-Alder Reaction
A diene reacts with a dienophile (most double or triple bonds) to give a cyclic compound (bicyclic if the diene is already cyclic) Electron Releasing Groups activate dienes, EWGs activate dienophiles
conformational isomers
- compounds that have the same mol. formula & same connectivity. They differ in respect of rotation around a single bond
- staggered vs. eclipsed
Nitrite
A nitrite is either a salt or an ester of nitrous acid.
Stereochemistry of Sn1 reaction
Nucleophile attacks either side of the carbocation.
Epoxide Reaction with Nucleophiles: Regioselectivity
Nucleophile opens epoxide ring from the back.
Regioselective: in unsymmetrical epoxides, the nucleophile attacks the less substituted C.
free-radical halogenation (4 steps)
1. initiation: can be initiated by light or heat
2. propagation: no net change in the # of radicals
3. termination: net decrease in the # of radicals. rxn continues until one of the reactive radicals of the propagation steps combines w/another radical
4. inhibition: rxn is inhibited by molecular oxygen. can happen ANYTIME, not necessarily after termination
The larger the energy of activation rate constant
The smaller the rate constant
Mechanism of Reaction of Alcohols with HX
More substituted alcohols usually react more rapidly with HX
The mechanism depends on the structure of the R group.
ester-----?-------1 -OH + 3 -OH
Gringard with 1. R-Mg-X, ehter/ 2. H3O
Nitrile Reaction with H2O
R-Cl + KCN --> R-CN -(H2SO4, H2O, Heat)-> R-COOH or R-CHO + HCN, KCN --> R-OH-CN -(H2SO4, H2O, Heat)-> R-COOH (Can stop at amide if controlled)
E2 Dehydration of 1 Alchols I
1 carbocations are highly unstable -> 1ROH do not undergo E1
1ROH undero dehydration by way of an E2 mech.
Valence Shell Electron Pair Repulsion Theory (VSEPR theory)
In covalent molecules both bonded and lone pairs of e- repel eachotherMolecules assume shape to keep all e- as far away frome each other as possibleSolid straight line is on planeSolid Wedge towards readerdash wedge away from reader
3 OH--------?------> most sub alkene is major + H2O
Dehydration H3O, THF This is an E1 mechanism
2 OH or 1 OH ------?------- Alkene (+OPOCl2)
POCl3/ pyridine this is an E2 mechanism
Methane
CH4
Na
NH3
Jones
CrO3, H2SO4+acetone
Reactive intermediate name
Radical
polar, neutral AAs
6
asparagine
cysteine
glutamine
serine
threonine
tyrosine
Sn1 number of steps
2
E1 on benzylic C
Yes
bond angles (ideal)
linear
trigonal planar
tetrahedral
180°
120°
109.5°
Solvent preference sn1
Polar protic solvents
Good nuc effect on Sn2
Accelerates
lipophilic
- lipid-loving
- synonym for hydrophobic
Ethylene
Ethylene is a chemical compound containing two carbons and four hydrogens. It is the simplest alkene.
A larger atom is (more/less) stable
more
Amide------?------> amine
1. LiAlH4, ether/ 2. H2O
Grignard
Reaction of an organometallic compound with a ketone to an alcohol
Atactic Polymer
Random configurations at each stereocenter
Destructive Interference
Two waves in different phase
Sulfide
The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of -2.
slowest
SN2 reaction with water as the nucleophile (slowest or fastest)
sp3 carbons are called "________ Carbons"
Allylic Carbons
Tertiarty -OH ------?---------> tertiary alkyl halide
(Sn1) HCl or HBr
What is a completely useless reaction for synthesis?
hydration
Acetoacetic Ester (AAE)
CH3-CO-CH2-CO-OEt can make substituted acetone by making enolate of AAE, alkylating, then saponification, acidification, and decarboxylation.
centrifugation
- separation by density
- for large macromolecules
Triangular planar
120°Three atoms bound to central atom with no lone pair
Gilman reagent
Gilman reagents are lithium and copper reagent compounds which are useful because they react with chlorides, bromides, and iodides to replace the halide group with an alkyl group.
Elimination reaction
Elements in the starting material are lost and a bond is formed
Summary of Sn2
Kinetics - Second-order kinetics; rate = k[ RX][Nu-]
Mechanism - one step
Stereochemistry - Backside attack of the nucleophile, inverison of configuration at a stereogenic center.
Identity of R - Unhindered halides react fastest
Capillary Action
Process by which the mobile phase moves up the stationary phase
Saponification
Hydrolysis of an Ester in aqueous base (consumes 1 mole base)
nucleophiles
- species that have unshared pairs of electrons or π bonds &, frequently, a neg charge
- electron pair donors
what affects BP
1. intermolecular forces
2. mass ∝ BP
3. branching ∝ BP⁻¹
Disulfide bond
A disulfide bond is a single covalent bond derived from the coupling of thiol groups.
Delta h on diagram
Determines the relative position of the reactants and products
Reactions of Epoxides
Epoxides do not contain a good leaaving group.
Epoxides do contain a strained three-membered ring with two polar bonds.
Epoxides can react with HX or with nucleophiles.
Amines (Mass Spec)
Beta-cleavage of 1o, 2o, and 3o aliphatic
column (flash) chromatography
- separates by polarity
- like TLC upside down & thru sand
protic solvent
A solvent that has a hydrogen atom bound to an oxygen as in a hydroxyl group or a nitrogen as in an amine group.
The higher the energy species stability
The less stable the species
Zaitsev's Rule
When an alchol has two or three beta carbons, dehydration is regioselective and follows Zaitsev's rule.
The more substituted alkene is the major product when a mixture of constitutional isomers is possible.
Ketone -----?------> 3 -OH
Gringard with 1. R-Mg-X, ether/ 2. H3O
judging basicity
- the more stable the anion, the less basic it is
- resonance stabilization or powerful e⁻ withdrawing grps will decrease basicity
If pKa is greater than the pH it is an (acid/base)
acid
Cis/Trans Differ in Physical Properties
Consequence of alkene polarity:
- cis and trans isomeric alkenes have different physical properties
- cis-2-butene b.p.: 4 C (net dipole) higher bp
- trans-2-butene b.p.: 1 C (no net dipole) lower bp
Molecular Ion Fragmentation
Gives a Cation and a Radical (only the cation is detected by the mass spec) (cation stability more important than radical stability)
peptide bonds vs. disulfide bridge
peptide bonds link AAs together into polypeptide chains
disulfide bridges link b/w cysteine R-groups
Regioselectivity of Epoxide Ring Opening
Ring opening of an epoxide with either Nu or HZ is regioselective becasue one constitutional isomer is the major or exclusive product.
The site selectivity of these two reactions is exactly opposite.
What mnemonic is used to calculate the strength of a base?
CARDIO
Charge - more neg, stronger base
Atom - Smaller the atom, stronger the base
Resonance - Least resonance, stronger the base
Dipole Induced - The further the EN atom is from the O, the stronger the base
O - Further the lone pair from the nucleus, stronger the base
Additon of Nitrogen Nucleophiles (Primary) to Carbonyls
Ammonia or 1o amines react with C=O to give imines (loss of H2O)
Oxidation of an alcohol yields what? If the resulting species is oxidized again, what is formed?
Oxidation is when we increase the # of bonds between C and O
Alcohol --> Aldehyde --> Carbox Acid
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