MCAT Organic Chemistry Quickies 1
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. What would you like to do?
Can you "resonate" onto a sp3 hybrydized atom?
What is the hybridization of a radical carbon?
What is radical inhibition?
When the free radical is inihibited by molecular oxygen. This forms a less reactive alkyl peroxy radical.
Which enantiomer is the primary product of halogenation?
Both leading to a racemic mixture (if unsymmetrical). The halogen can attack from bottom or top of the sp2 hybdrized carbon.
Radical and carbocation stability
methyl < 1 < 2 < 3
Is bromination or chlorination more selective?
- Bromination - favors tertiary
- Chlorination - less selective because its greatly exothermic
Better nucleophile trend
- Negative charge on the least electronegative atom (C- > N- > O- > X-)
- Carbon is greatest nucleophile because it is not electronegative enough to hold the extra pair of electrons (-) as oxygen can so it is a highly reactive nucleophile
Remember the possibility of hydride and methyl shifts!
What are nucleophiles?
- Nucleophiles - have unshared pairs of electrons, partial negative, electron pair donors, lewis base/ligand
- N strength increases as negative charge increases
- N strength increases going down the period (F<Cl<Br<I)
- N strength increases going left in the period (OH < NH < C)
- basically, the less electronegative and more negative the charge, the stronger the nucleophile
Electrophiles are lewis acids or bases?
SN2 mechanism characteristics
- reactivity: CH3 > 1 > 2 >3
- stereochem: Inversion of stereochemistr due to backside attack
- kinetics: rate = k [nucleophile][electrophile] - second order
- solvent: polar aprotic
- rearrangement: no rearrangements b/c no carbocation formatoin
- favored conditions: strong, non-bulky nucleophile
SN1 mechanism characteristics
- reactivity: 3 > 2 > 1 > methyhl
- sterochem: racemate
- kinetics: rate: k[electrophile] - carbocation formation
- solvent: polar protic - stabilize carbocation
- rerrangements: possible to make more stable carbocation
- favored conditions: non-basic, weak nucleophiles
Can ethers form intermolecular H bonds?
No, becuase it does not have H attached to NOF atoms, but it can H bond with water and other atoms with H
In an amide bond, what is the hybdrizatoin of the N group?
sp2 because it can participate in resonance with the adjacent carbonyl group
- formation of carbocation b/c leaving group leaves first
- need beta hydrogens. if no adjacent hydrogens are available, eliminaiton cannot occur
- reactivity: 3 > 2 >>>> 1
- stereochemistry: most substituted favored. trans over cis
- kinetics: rate: k[haloalkane]
- solvent: protic
- rearrangemenst: possible!
- favoring conditions: weak base and high temp
- stereochem: anticoplanar or trans diaxial
- reactivity: 3 > 2 > 1
- reactoin rate: k[base][substrate]
- solvent: polar aprotic
- arrangements: nope
- favoring conditions: strong bulky bases, high temp
The stronger the acid....
- The more stable the conjugate bas
- electron withdrawing groups and the ability to resonate stabilize the conjugate base
- electron donating groups would destabilize = stronger base, weak acid
- usually with pi bonds
- beaware of enantiomer formations and other stereochem such as hindrance
- markovnikov and anti
3 alkane + H2SO4/H2O
forms an alcohol
Reactoins that result in antimarkovnikov
- hydroboration (1. BH3/B2H6, 2. H2O2)
- HBr addition with peroxides
Oxidation of pi bonds with Dilute KMnO4
Syn addition of diol
- 1) H2 with Ni, Pd, Pt = syn addition of H2
- 2) Alyne + lindlar catalyst with Pd = syn addition of H-H across pi bond resulting in cis - stops hydrogenation reduction of alkyne at alkene stage
- 3) Na, NH3 + alykne = trans alkene. does not reduce alkenes
Double bond to carbonyl gruop (ketone or aldehyde possible)
- 4n+2 = number of pi electrons
- n = whole number
- Ring activators
- Donate a pair of electrons
- R groups
- Halogens are O,P but deactivating
- - NR3, N02, CN
- - things that pull electrons
Which is more stable keto or enol
- need a hydrogen to remove. so if you have a tertiary alcohol, you cannot oxidize it
- some oxidizing agents include chromates, conc nitritic acid, oxygen
- requires alpha hydrogens
- results in alpha beta unsaturated ketone where the C=C bond is between the alpha and beta carbons
- the c=c is more electrophilic, so nucleophiles will attack c=c first then resonate to form enol which can tautoremize to a more stable keto form - this is called michael addition
carbonyl to alcohol even with good leaving group
Michael addition (post aldol condensation)
- remember, the oxygen and double bond can undergo keto-enol tauto (keto is favored)
Thermodynamic vs kinetic product
thermodyanamic is most stable
What type of carboxylic acids are prone to decarboxylations?
Those that have carbonyl groups beta to the carboxylate
Carboxylic acid + alcohol =?
Extractions seperate based on:
- ions tend to dissolve in the aq layer. As a result, you use acid bases
- NaOH would deprotenate a weak acid
- HCO3 would deprotenate a strong acid
- This allows one to separate a strong acid from strong base
In TLC, is the plate polar or nonpolar?
Polar - allows nonpolar materials to travel up further while polar substancs would stick to the plate
Fractional vs simple distillation?
Fractional allows for the separation of substances with similar boiling poitns
How many Ka's does an amino acid have?
2 COOH and NH3 groups
Isolectric point. Define.
The point where the amino acid acts as a zwitterion which has a net neutral charge. The pI is also the equivalence point.
What does benedicts solution detect?
- Detects carbonyl units of sugars
- Hemiacetals = positive test (plain glucose)
- Glycogen = weakly positive (only the end points are hemiacetals)
- Benedicts solution is an oxidized form of copper - this gets reduced by the sugars (Cu2+ to Cu+) - this oxidizes the sugar in return.
- The anomeric carbon in glucose gets oxidized.
What are the two anomers of glucose?
- Alpha - OH pointing down
- Beta - OH pointing up
- Mutorotation = conversion b/w both (has to go through the chain formula)
what type of bonds are between nucleic acids
gem vs vic
- gem - 2 X or 2 OH on same carbon
- vic - 2 X or 2 OH on adjacent carbons (nipple piercings
What would you like to do?
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