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Organic Chemistry Ch. 4 - Analyzing Organic Reactions
MCAT
23
Organic Chemistry
Undergraduate 2
05/30/2016

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Term

How do you calculate the acid dissociation constant?

pKa?

Definition

Ka = [H+][A-]/[HA]

pKa = -logKa

Term
How do you tell acidity and basicity from pKa?
Definition
more acidic molecules will have a smaller or even negative pKa; more basic molecules will have a larger pKa; a higher pKa molecule with have a weaker conjugate base and a lower pKa molecule will have a stronger conjugate base
Term
How do you compare/determine nucleophilicity?
Definition
  • charge: nucelophilicity increases with increasing electron density (more negative charge)
  • electronegativity: nucleophilicity decreases as electronegativity increases because these atoms are less likely to share electron density
  • steric hindrance: bulkier molecules are less nucleophilic
  • solvent: protic solvents can hinder nucleophilicity by protonating the nucleophile or through hydrogen bonding
Term
What makes a solvent protic or aprotic?
Definition
protic solvents can hydrogen bond, aprotic solvents can't
Term
How does the solvent affect the nucleophilicity of a molecule?
Definition
In an polar protic solvent nucleophilicity increases down the periodic table because the more electronegative atoms will form bonds with the protons making it harder for them to access the electrophile; in polar aprotic solvents nucleophilicity increases up the periodic table because because there are no protons to get in the way
Term
What factors affect electrophilicity?
Definition
  • the more positive charge the more electrophilic
  • a molecule with empty orbitals (unhybridized) is a better electrophile because the nucleophiles can make a bond without displacing the leaving group
  • a better leaving group makes for a better electrophile
Term
leaving groups
Definition
  • molecular fragments that retain the electrons after heterolysis
  • the best leaving groups can stabilize additional charge through resonance or induction
  • weak bases (the conjugate bases of strong acids) make good leaving groups
  • alkanes and hydrogen ions are almost never leaving groups because they form reactive anions
Term
nucleophilic substitution reactions
Definition
a nucleophile forms a bond with a substrate carbon and a leaving group leaves
Term
unimolecular nucleophilic substitution reactions
Definition
  • 2 steps
  • carbocation formation
  • occurs at most substituted carbocation due to stability
  • first order reaction
  • product is racemic mixture due to planar carbocation
Term
biomolecular nucleophilic substitution reactions
Definition
  • single step reaction
  • backside attack 
  • concerted reaction
  • must have strong nucleophile and substrate can't be sterically hindered
  • less substituted carbons (primary carbons)
  • second-order reaction
  • if nucleophile and leaving group have same priorities in their respective molecules the absolute configuration changes from S to R and R to S
Term
What makes a good oxidizing agent?
Definition
  • high affinity for electrons
  • unusually high oxidiation states
Term
PCC
Definition
  • primary alcohol to aldehyde
  • secondary alcohol to ketone
Term
CrO3/pyridine
Definition
  • primary alcohol to aldehyde
  • secondary alcohol to ketone
Term
H2CrO4
Definition
  • aldehyde to carboxylic acid
  • primary alcohol to carboxylic acid
  • secondary alcohol to ketone
Term
KMnO4
Definition
  • aldehyde to carboxylic acid
  • primary alcohol to carboxylic acid
  • secondary alcohol to ketone
  • methylbenzene to benzoic acid
Term
H2O2
Definition
aldehyde to carboxylic acid
Term
alkene to aldehyde/ketone
Definition
  • O3, then Zn
  • O3, then CH3SCH3
Term
O3, then H2O2
KMnO4, heat, H3O+
What do both of these do?
Definition
  • alkene to carboxylic acid/ketone
  • alkyne to carboxylic acid
Term

OsO4

or

KMnO4, HO-

 

Definition
alkene to diol
Term
mCPBA
Definition

 cis alkene to epoxide

ketone to ester

Term

NaIO4 or

Pb(OAc)4 or

HIO4

 

Definition
diol to an aldehydes and ketones
Term
LiAlH4
Definition
strong reducing agent; reduces an aldehyde, ketone, carboxylic acid or amide down to an alcohol or amine; reduces an exter to two primary alcohols
Term
Both nucleophile-electrophile and oxidation-reduction reactions tend to act at the highest priority (most oxidized) functional group
Definition
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