O Chem Flashcards
SN1 vs. SN2 reactions?
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
What are the re-dox levels of organic molecules?
Most reduced - alkane - alcohol - aldehyde (from prim. alc), ketone (from secondary alc) - carboxylic acid - CO2 Most oxidized
NO RXN FOR A TERTIARY ALCOHOL
What is a strong/weak oxidizing agent?
Strong: KMnO4 – can oxidize all the way to carboxylic acid
Weak: PCC – can only oxidize to an aldehyde
What is a strong/weak reducing agent?
Strong: LiAlH4/NaBH4 – can reduce all the way to alcohol
Weak:
In terms of bonds what does reduction/oxidation do?
Reduction: increase in C-H bonds, decrease in C-O bonds
Oxidation: Increase in C-O bonds, decrease in C-H bonds
What is a nucleophile? What makes a strong nucleophile?
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
What is an electrophile? What makes a strong electrophile?
High positive charge
High acidity
High electronegativity
What makes for a good leaving group?
A molecule that can stabilize it’s extra electrons well (high electronegativity)
Weak bases and strong acids can do that
Protic vs. aprotic solvents?
Protic: can H bond
- carboxylic acids, ammonia/amines, water/alcohols
Aprotic: can’t H bond
- DMF, DMSO, acetone
What are the main IR spectroscopy peaks to know?
C=O: 1750 (sharp peak)
OH: 3300 (broad peak). NH: 3300 (sharp peak)
What does UV spectroscopy measure?
Conjugated systems/double bonds
What is downfield/upfield? Deshielding? Peak height? in NMR
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
What does mass spectrometry measure?
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
What are the IUPAC naming conventions/rules?
1) identify longest carbon chain
2) number chain starting closest to highest priority functional group
3)
What does alpha, beta refer to?
Epimers at the anomeric carbon
What is the guiding rule of extractions? What layers does it form? How can you increase product?
Like dissolves like
- NP solvent to dissolve NP solute
Aqueous layer: water
Organic layer: non-polar
Repeat extractions to maximize product
What is distillation? Simple vs. vacuum vs. fractional?
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
What are the basics of chromatography? TLC? Reverse-phase? Rf value?
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)
Ion exchange? Size exclusion? Affinity?
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
What is gas chromatography?
Lower BP = faster elution
Higher BP = greater retention/slower elution
Uses a computer generated chart that peaks when something elutes
What is HPLC?
Stationary phase: polar
Mobile phase: non polar
Difference is that it is computerized like gas chromatography
What is gas-liquid chromatography?
Mobile phase: gas
Stationary phase: liquid
Low BP elutes first
High BP elutes last
How do you determine the number of peptides per amino acid?
n! (n = #of amino acids)
What are structural/constitutional isomers?
same molecular formula but different connectivity and different chemical properties
What are stereoisomers? What are the types of stereoisomers?
Same molecular formula and connectivity but differ in their spatial arrangement
Includes conformational isomers and configurational isomers
What is a conformational isomer?
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
What is a configurational isomer?
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
What is chirality? R, S configuration?
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
What is E, Z?
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
