Flashcards in this deck (53)

• What is a nucleophile?

  An electron-pair donor that attacks electron-deficient carbons.
  chemistry nucleophile
• What is a leaving group (LG)?

  An atom or group that departs with the bonding electrons in a substitution or elimination reaction.
  chemistry leaving_group
• What is the difference between SN1 and SN2 reaction mechanisms?

  • SN1: two-step unimolecular reaction with carbocation intermediate
  • SN2: one-step bimolecular reaction with backside attack
  chemistry reaction_mechanisms
• Which step is rate determining in SN1 reactions?

  The unimolecular leaving group departure forming the carbocation.
  chemistry rate_determining
• What stereochemical outcome is expected from SN1?

  Racemic mixture due to nucleophile attack on planar carbocation intermediate.
  chemistry stereochemistry
• What stereochemical outcome is expected from SN2?

  Inversion of configuration (Walden inversion) due to backside attack.
  chemistry stereochemistry
• What is molecularity in a reaction?

  The number of species involved in the rate determining step.
  chemistry molecularity
• What is the molecularity of SN1?

  Unimolecular (depends only on the substrate).
  chemistry molecularity
• What is the molecularity of SN2?

  Bimolecular (depends on both substrate and nucleophile).
  chemistry molecularity
• Write the rate law for an SN1 reaction.

  rate = k [substrate]
  chemistry rate_law
• Write the rate law for an SN2 reaction.

  rate = k [substrate][nucleophile]
  chemistry rate_law
• Order carbocation stability from most to least stable.

  • Tertiary
  • Secondary
  • Primary
  • Methyl
  chemistry carbocation stability
• What effect do alkyl groups have on carbocation stability?

  Alkyl groups stabilize carbocations through electron donation (induction and hyperconjugation).
  chemistry alkyl_groups stability
• What type of mechanism is favored by methyl and primary alkyl halides?

  SN2
  chemistry reaction_mechanism
• What reaction mechanism is favored by tertiary alkyl halides?

  SN1
  organic reaction_mechanism
• Which mechanism is favored for secondary alkyl halides?

  Both SN1 and SN2 depending on conditions.
  organic reaction_mechanism
• How does steric hindrance affect SN2 reactions?

  Slows or prevents SN2 by blocking backside attack.
  organic sterics
• What type of solvent favors SN1 reactions?

  Polar protic solvents (can hydrogen bond and stabilize ions).
  organic solvents sn1
• What type of solvent favors SN2 reactions?

  Polar aprotic solvents (increase nucleophilicity).
  organic solvents sn2
• List common polar aprotic solvents.

  • Acetone
  • Acetonitrile (MeCN)
  • DMF
  • DMSO
  • HMPA
  • THF
  organic solvents
• In polar protic solvents, which nucleophile is strongest: F-, Cl-, Br−, or I−?

  I- (fluoride is highly solvated and less nucleophilic)
  organic nucleophiles
• In polar aprotic solvents, which nucleophile is strongest: F-, Cl-, Br−, or I−?

  F- (smaller size and lack of solvation increases strength)
  organic nucleophiles
• What is defined as a stereogenic (chiral) center?

  A carbon with four different substituents and no plane of symmetry.
  organic chirality
• What are enantiomers?

  Non-superimposable mirror image stereoisomers.
  organic stereochemistry
• What physical properties do enantiomers share?

  Same melting point, boiling point, solubility — except optical rotation.
  organic properties
• What is a racemic mixture?

  A 1:1 mixture of enantiomers; optically inactive.
  organic mixtures
• Define diastereomers.

  Stereoisomers that are not mirror images; have different physical properties.
  organic stereochemistry
• What is a meso compound?

  A molecule with stereogenic centers but an internal plane of symmetry, making it achiral.
  organic chirality
• How do you assign R/S configuration?

  1. Prioritize groups by atomic number
  2. Orient lowest priority back
  3. Trace path 1→2→3
  4. Clockwise = R
  5. Counterclockwise = S
  chemistry stereochemistry
• What happens to R/S assignment if the lowest priority substituent is in front?

  Assign as normal and then invert the designation.
  chemistry stereochemistry
• How do you generate an enantiomer from a molecule in drawing?

  Make one exchange of any two substituents around the stereocenter.
  chemistry stereochemistry
• How do you interconvert between wedge/dash and Fischer projections?

  • Horizontal bonds are wedges (coming out)
  • Vertical bonds are dashes (going back).
  chemistry projections
• What is Walden inversion?

  The inversion of stereochemistry at the carbon center during SN2 backside attack.
  chemistry stereochemistry
• How does a good leaving group affect reaction rate?

  Improves rate of both SN1 and SN2 by facilitating bond breaking.
  chemistry reaction_kinetics
• Does the nature of the leaving group determine the mechanism?

  No, better leaving groups speed up both mechanisms but do not change pathway preference.
  chemistry reaction_mechanisms
• What is hyperconjugation?

  A stabilization involving delocalization of electrons from adjacent C–H or C–C sigma bonds into an empty p orbital of carbocation.
  chemistry organic
• What is the main cause of nucleophilicity trend differences in protic vs aprotic solvents?

  Solvation shells—small ions are more strongly solvated in protic solvents, reducing nucleophilicity.
  chemistry solvents
• Why is SN2 unfavorable on tertiary carbons?

  Steric hindrance prevents nucleophile from backside attack.
  chemistry reaction_mechanisms
• What is the primary determining factor for SN1 vs SN2 on secondary carbons?

  Reaction conditions: solvent, nucleophile strength, sterics.
  chemistry reaction_mechanisms
• What is enantiomeric excess (ee)?

  The difference in percentage between two enantiomers in a mixture; ee = %major - %minor.
  chemistry stereochemistry
• How many stereoisomers exist for a molecule with n stereogenic centers ignoring meso?

  2^n.
  chemistry stereochemistry
• What effect does a polar protic solvent have on carbocations?

  It stabilizes carbocations via hydrogen bonding and solvation.
  chemistry solvents
• How does increasing nucleophile concentration affect the rate of an SN2 reaction?

  It increases the rate because nucleophile participates in the rate-determining step.
  chemistry sn2
• What effect does increasing substrate concentration have on the rate of an SN1 reaction?

  It increases the rate because substrate concentration controls the unimolecular RDS.
  chemistry sn1
• What is meant by a transition state?

  A high-energy, unstable configuration during a reaction where bonds are partially broken and formed.
  chemistry reaction_mechanisms
• How does a catalyst affect a reaction?

  It lowers the activation energy, increasing the reaction rate without being consumed.
  chemistry catalysis
• What is a carbocation intermediate?

  A positively charged carbon species formed during SN1 reactions that is planar and sp2 hybridized.
  chemistry intermediates
• What is backside attack in SN2?

  Nucleophile attacks the opposite side of the leaving group, causing inversion.
  chemistry sn2
• How are enantiomers separated if they have identical physical properties?

  Convert one to a diastereomer which can be separated due to different physical properties.
  chemistry enantiomers
• What is meant by a sterically hindered nucleophile or base?

  A nucleophile or base too bulky to easily approach the electrophilic center or proton.
  chemistry nucleophiles
• What reagent converts an alkene to an epoxide?

  Peroxyacids like MCPBA (meta-chloroperoxybenzoic acid).
  chemistry reagents
• What stereochemical outcome does epoxidation of cis and trans alkenes give?

  Cis alkenes give cis epoxides; trans alkenes give trans epoxides.
  chemistry epoxidation
• What reagents convert alkenes to syn 1,2-diols?

  Common reagents include OsO4 (osmium tetroxide) and KMnO4 (potassium permanganate).
  chemistry reagents