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MCAT > O Chem > Flashcards

O Chem Flashcards

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MCAT flashcards
1
Q

SN1 vs. SN2 reactions?

A

SN1: unimolecular
1) RDS when LG leaves forming a carbocation
2) then nucleophilic attack on the carbocation
- forms a racemic mixture (can attack on either side of
carbocation)
- the more substituted the carbon atom the more stable
the carbocation so faster reaction rate (EDG’s)

SN2: bimolecular
1) nucleophilic attack and LG leaves one step
- causes an inversion in stereochemistry
- requires a strong nucleophile and non-sterically
hindered carbon

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2
Q

What are the re-dox levels of organic molecules?

A 
Most reduced
 - alkane
 - alcohol
 - aldehyde (from prim. alc), ketone (from secondary alc)
 - carboxylic acid
 - CO2
Most oxidized

NO RXN FOR A TERTIARY ALCOHOL

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3
Q

What is a strong/weak oxidizing agent?

A

Strong: KMnO4 – can oxidize all the way to carboxylic acid

Weak: PCC – can only oxidize to an aldehyde

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4
Q

What is a strong/weak reducing agent?

A

Strong: LiAlH4/NaBH4 – can reduce all the way to alcohol

Weak:

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5
Q

In terms of bonds what does reduction/oxidation do?

A

Reduction: increase in C-H bonds, decrease in C-O bonds

Oxidation: Increase in C-O bonds, decrease in C-H bonds

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6
Q

What is a nucleophile? What makes a strong nucleophile?

A 
High negative charge
High basicity 
Low electronegativity (doesn't hold negative charge well so it attacks)

Nucleophilic attack so don’t want it to be bulky

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7
Q

What is an electrophile? What makes a strong electrophile?

A

High positive charge
High acidity
High electronegativity

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8
Q

What makes for a good leaving group?

A

A molecule that can stabilize it’s extra electrons well (high electronegativity)

Weak bases and strong acids can do that

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9
Q

Protic vs. aprotic solvents?

A

Protic: can H bond
- carboxylic acids, ammonia/amines, water/alcohols

Aprotic: can’t H bond
- DMF, DMSO, acetone

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10
Q

What are the main IR spectroscopy peaks to know?

A

C=O: 1750 (sharp peak)

OH: 3300 (broad peak). NH: 3300 (sharp peak)

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11
Q

What does UV spectroscopy measure?

A

Conjugated systems/double bonds

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12
Q

What is downfield/upfield? Deshielding? Peak height? in NMR

A 
Left = downfield
Right = upfield

Deshielding: when electron density is pulled away

  • EWG will be downfield
  • EDG will be upfield

Height of NMR peak is proportional to the number of protons and each peak is a distinct set of equivalent protons

Peak number = n+1 where n = # of adjacent protons

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13
Q

What does mass spectrometry measure?

A

Mass abundance vs. m/z ratio

Higher peak = higher abundance at that mass

m/z differences b/w peaks identifies the mass of those fragments

Multiple peaks w/ same m/z signifies cis/trans isomers

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14
Q

What are the IUPAC naming conventions/rules?

A

1) identify longest carbon chain
2) number chain starting closest to highest priority functional group
3)

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15
Q

What does alpha, beta refer to?

A

Epimers at the anomeric carbon

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16
Q

What is the guiding rule of extractions? What layers does it form? How can you increase product?

A

Like dissolves like
- NP solvent to dissolve NP solute

Aqueous layer: water
Organic layer: non-polar

Repeat extractions to maximize product

17
Q

What is distillation? Simple vs. vacuum vs. fractional?

A

Separating two liquids by their boiling points

Simple:

  • used for separating lower boiling point liquids
  • and large difference in boiling point
  • > 25 celcius difference, <150 celcius boiling point

Vacuum:
- for higher boiling point liquids
- vacuum reduces external pressure so temp required
to reach vapor pressure = external pressure is lower

Fractional:
- for close boiling point liquids
- objects are placed in column to increase surface area
- vapor condenses then refluxes back down and is
evaporated by rising heat

18
Q

What are the basics of chromatography? TLC? Reverse-phase? Rf value?

A

Basics: has a stationary and mobile phase, depending on which phase the compound is more attracted to it will travel different distances

TLC

  • stationary phase: silica gel (very polar)
  • mobile phase: something non-polar
  • used for assessing purity

Reverse-phase

  • stationary phase: non-polar
  • mobile phase: polar

Rf value = distance spot moved / distance solvent front moved (higher rf value means more attracted to mobile phase)

19
Q

Ion exchange? Size exclusion? Affinity?

A

All forms of column chromatography

Ion exchange:

  • anion-exchange: binds negative charges
  • cation-exchange: binds positive charges
  • repelled charge elutes first

Size exclusion:
- contains beads that have tiny pores that small
compounds enter and travel through
- large compounds don’t enter pores and elute first

Affinity:
- beads are coated w/ a receptor/antibody that binds a
specific protein and retains it

20
Q

What is gas chromatography?

A

Lower BP = faster elution
Higher BP = greater retention/slower elution

Uses a computer generated chart that peaks when something elutes

21
Q

What is HPLC?

A

Stationary phase: polar
Mobile phase: non polar

Difference is that it is computerized like gas chromatography

22
Q

What is gas-liquid chromatography?

A

Mobile phase: gas
Stationary phase: liquid

Low BP elutes first
High BP elutes last

23
Q

How do you determine the number of peptides per amino acid?

A

n! (n = #of amino acids)

24
Q

What are structural/constitutional isomers?

A

same molecular formula but different connectivity and different chemical properties

25
Q

What are stereoisomers? What are the types of stereoisomers?

A

Same molecular formula and connectivity but differ in their spatial arrangement

Includes conformational isomers and configurational isomers

26
Q

What is a conformational isomer?

A

A stereoisomer that differs in rotation along a sigma bond

Think:
- chair conformation vs. cyclic conformation
- wedge is up, dash is down, and bulkiest at equatorial
position
- fisher projection
- cis: same side, and trans: different side

27
Q

What is a configurational isomer?

A

A stereoisomer that requires breaking bonds to interconvert

Diastereomer: non-mirror image
- 2^n (n = # of chiral centers)
- different at some chiral centers
- different properties
- epimer: diastereomer that differ in configuration at
one position
- cis/trans is a type of diastereomer

Enantiomer: non-superimposable mirror image
- different at every chiral center
- optically active
- identical properties
- refers to L, D (molecule w/ multiple chiral centers) L is
more common

28
Q

What is chirality? R, S configuration?

A

Chiral center: sp3 carbon attached to four different substituents (+) and (-) are associated w/ chirality

R, S: for a single chiral center

1) assign priority w/ highest atomic weight being 1
2) re-arrange so lowest priority group is in the back (H is on a dash)
3) Trace from 1 –> 2 –> 3 priority, CW is R, CCW is S
4) If H isn’t in the back then flip the R,S

29
Q

What is E, Z?

A

Configuration for compounds w/ double bonds

E: if two highest priority are on opposite sides of bond
Z: if two highest priority are on same side of bond

MCAT (7 decks)

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