Experiment 6: Alkyl Halides

• What are alkyl halides?


  Organic molecules containing a halogen atom bonded to an sp3 hybridized carbon atom
• What is the polarization of the functional group in alkyl halides?


  The carbon is electrophilic and the halogen is nucleophilic
• What is an electrophile?


  A molecule or ion that accepts a pair of electrons to make a new covalent bond
• What is a nucleophile?


  A molecule or ion that donates a pair of electrons to form a new covalent bond
• What does the dipole moment in alkyl halides indicate?


  It indicates a partially positive charge on carbon and a partially negative charge on halogen
• What is the general molecular formula for alkyl halides?

  CnH2n+1X
• How are alkyl halides classified based on the carbon atom to which the halogen is bonded?


  They are classified as primary, secondary, and tertiary alkyl halides
• What characterizes a primary alkyl halide?


  A carbon atom attached to one R group and two hydrogens
• What characterizes a secondary alkyl halide?


  A carbon atom attached to two R groups and one hydrogen
• What characterizes a tertiary alkyl halide?


  A carbon atom attached to three R groups and no remaining hydrogen
• What are the physical properties of alkyl halides?


  • Higher boiling and melting points than alkanes with the same number of carbons
  • Boiling and melting points increase with larger R groups
  • Boiling and melting points increase with larger halogens
  • Soluble in organic solvents, insoluble in water
• Why do alkyl halides have higher boiling and melting points than alkanes?


  Due to the presence of halogens
• How does the size of R affect the boiling and melting points of alkyl halides?


  Larger surface area leads to higher boiling and melting points
• How does the size of the halogen (X) affect the boiling and melting points of alkyl halides?


  More polarizable halogens lead to higher boiling and melting points
• What is the result of an elimination reaction in alkyl halides?


  A new pi-bond is formed by the elimination of a halide ion and another atom
• What happens during a nucleophilic substitution reaction?


  The nucleophile displaces the leaving group from the carbon atom
• What does SN2 stand for?


  Substitution nucleophilic bimolecular
• What does bimolecular mean in the context of SN2 reactions?


  The transition state involves the collision of two molecules
• What factors affect the rate of an SN2 reaction?


  The concentration of both the nucleophile and electrophile
• What characterizes the mechanism of an SN2 reaction?


  It is a concerted reaction with simultaneous backside attack and leaving group expulsion
• What is the result of a backside attack in an SN2 reaction?


  The product will be an inversion product
• How does the number of R groups affect the rate of an SN2 reaction?


  As the number of R groups increases, the rate of the SN2 reaction decreases
• Which alkyl halides undergo SN2 reactions easily?


  Methyl and 1° alkyl halides
• Which alkyl halides react more slowly in SN2 reactions?


  2° alkyl halides
• Which alkyl halides do not undergo SN2 reactions?


  3° alkyl halides
• What does SN1 stand for?


  Substitution nucleophilic unimolecular
• What does unimolecular mean in the context of SN1 reactions?


  The nucleophile is not present in the rate determining step
• What is the rate determining step (RDS) in an SN1 reaction?


  It is the slow step where the electrophile undergoes a reaction
• What is the first step in an SN1 reaction?


  Formation of a carbocation
• What is required for the formation of a carbocation in an SN1 reaction?


  The leaving group must be a weak base
• What is the best weak base for the leaving group in an SN1 reaction?


  The halogen
• What happens in the second step of an SN1 reaction?


  The nucleophile attacks the carbocation
• What type of solvent is used in SN1 reactions?


  Polar protic solvents
• What characterizes polar protic solvents?


  They have electronegative atoms with ionizable protons
• What is formed when the nucleophile Br- attacks the carbocation?


  An acid is formed, specifically HBr
• What happens to the oxygen in the polar protic solvent during the SN1 reaction?


  It becomes negatively charged and has lone pairs
• What types of products can be formed from the nucleophilic attack in an SN1 reaction?


  A mixture of retention product and inversion product
• How does the stability of the carbocation affect the rate of an SN1 reaction?


  The more stable the carbocation, the easier the reaction proceeds
• Which alkyl halides undergo SN1 reactions rapidly?


  3° alkyl halides
• Which alkyl halides yield positive results in SN1 reactions but react more slowly?


  2° alkyl halides