Chapter 10-Organic Chem Flashcards
SN1 Unimolecular or Bimolecular?
Unimolecular = only 1 species involved in RDS
Mechanism of SN1 (2)
1) Heterolytic fission of C-X bond to produce = acts an an intermediate (RDS)
2) Carboncation reacts rapidly w/ hydroxide ion to yield final product
Hydrolysis of Halogenoalkanes to Alcohol: mechanism + conditions
R-X + H2O → R-OH + HX
+ Heat under reflux w/ sodium or potassium hydroxide
+ Solvent of 50/50 water and ethanol
→ Cuz halogenoalkane insoluble in water
SN2 Unimolecular of Bimolecular?
Bimolecular = 2 species affecting the RDS
→ Halogenoalkane and the nucleophile
SN1 and SN2 which one is primary and which one tertiary?
SN1 = Tertiary (big and bulky so needs 2 step process) SN2 = Primary (smaller, less stable so one step process is OK)
SN2 RDS?
Attack of hydroxide ion on the halogenoalkane
SN2 transition state?
When the bond to Nu- starts to form at the same time as the bond to X broken!
Halogenoalkanes exists as what type of isomers?
Stereoisomers because there are 4 different groups attached to the carbon atom (w/ the Halogen)
Halogenoalkanes can exist as?
A pair of enantiomers
SN2 → start with one PURE enantiomer what is the product?
PURE enantiomer with inverted configuration
SN1 what type of carboncation formed?
Planar carboncation intermediate
→ Nu- can attack on either side of it
What mixture does SN1 mechanism result in?
Racemic mixture
= cuz there are EQUAL prob. of both attacks of the Nu-
Which mechanism does secondary halogenoalkanes use?
Both SN1 and SN2
How does the nature of the X also affects the mechanism choice? (2)
1) Polarity of the C-X bond
→ decreases from Cl to I = decreases the susceptibility of the C to a SN2 attack cuz the partial + charge on the C would be smaller
2) Strength of the C-X bond
→ decrease from Cl to I = so the bonds in the 1st step of SN1 breaks more easily w/ I
Which Halogen does SN1 and SN2 prefer?
SN1 = Iodine SN2 = Chlorine Bromine = both mechanisms can occur
Solvents that SN1 prefers?
+ Polar s.a water and alcohol
→ cuz they can solvate the ions formed by heterolytic fission
+ Protic = can H.bond cuz they contain a H bonded to and O or N → they often bind to nucleophiles making SN2 less favourable.
Solvents that SN2 prefers?
+ Polar = so that solvent can bond to leaving group and it can dissolve in them
+ Aprotic
→ so don’t solvate nucleophile
Which reaction occurs faster SN1 or 2
SN1 is faster!
→ so factors that favour SN1 tend to increase the rate of reaction
What species undergo Electrophilic addition reactions and how many steps is it?
+ Alkenes
+ 2 step process
What do Electrophiles act as?
+ Lewis Acids = electron pair acceptor
+ attacks region of high electron density
→ double bonds or triple bonds
What are Electrophiles?
Electron deficient species = Electron LOVIN’ <3
→ Either has a formal + charge or has a partial + charge due to the presence of highly electronegative specie.
Examples of non-symmetrical electrophiles (2)
H-Br / I-Cl
Which one attacks the Alkene in a non-symmetrical electrophile?
The one with the more + charge = the one with the less electronegativity
List the carboncations in order of stability (more stable first):
Secondary
Primary
Tertiary
Tertiary (most stable) > Secondary > Primary
What makes a carboncation species more stable?
The lower the electrical charge on the C atom
Inductive effect
The effect of a funct. group or atom in an organic molecule in attracting (sigma electrons) towards itself OR repelling them
→ results in the formation of a dipole molecule
When an electrophile attacks a non-symmetrical alkene which carboncation predominates leading to the major product?
The more stable one
Markovnikov’s Rule? →
used to predict the Maj. product of the Electrophilic addition of hydrogen Halides (H-X) to unsymmetrical alkenes
“Hydrogen atoms will preferentially bond to the C atom of the alkene already has most hydrogens attached to it in a double bond”
Reduction reactions depend on what?
Reagents that can donate a hydride ion (H-) to a molecule
