11843021
Description
Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
over 6 years ago
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| Question | Answer |
| What is the halogenation radical reaction? | Homolytic fission CH4+4Cl2->CCl4+4HCl |
| Write the initiation, propagation and termination reaction | Cl2->Cl.+.Cl CH4+cl.->CH3. +HCl CH3.+Cl2->CH3Cl + Cl. Any free rads meeting |
| What does an excess of Cl/CH4 yield? | CCl4 CH3Cl |
| Describe the IUPAC of naming haloalkanes | Can be covalently bonded to 1'/2'/3' alkanes |
| Describe electronegativity of halogens | As you go across the period electronegativity increases Have an additional proton as you go across, can attract electrons better Electronegativity increases up a group, fewer electron shells, less shielding Forms polar bonds with carbon, has dipoles |
| Describe the polarity of halogens | Forms polar bonds with carbon, has dipoles, bigger dipoles as you go up the group |
| What are the 2 reaction types of haloalkanes? | Nucleophilic substitution Elimination, where nucleophile acts as a base |
| What is the SN1 mechanism? | Halide ion lost first left with carbocation Nucleophile attacks the carbocation Heterolytic mechanism - both electrons go to Br unimolecular nucleophilic substitution |
| What is the SN2 mechanism? | Direct displacement Nucleophile attacks, forms an intermediate transition state, then halide is displaced bimolecular nucleophilic displacement |
| What is the rate of SN2 dependant on? | [nuc] [c skeleton] 2nd order as we're dependant on 2 different concentrations S=Sub N=Nuc 2=2 order |
| What is a Walden Inversion? | Orientation of molecule "flips" from facing halide to facing nucleotide Transition state forms |
| Describe changes in structure of SN1 | Goes from tetrahedral to trigonal planar intermediate, so has sp2 hybridisation, as halide has taken the electrons there's an empty P orbital above and below the carbon Carbon is charged |
| How many steps does SN1 have? | 2 steps, so 2 transition states 1 transition state formation is the slowest reaction and the rate limiting step Reaction is 1st Order dependence on electrophile, zero order dependence on nucleophile So r=k[reactant] moles l-1 s-1 |
| Describe the stereochemistry of SN1 mechanism | Nucleophile can attack top or bottom of planar molecule, so groups are going to flip up or down depending on the direction of attack Forms enantiomers |
| What determines whether SN1 or SN2 happens? | Most important is the carbon skeleton Compounds that can form a stable cabocation generally react by SN1 |
| What influences carbocation stability? | Number of substituents and accessibility of the carbon for nucleophilic attack e.g. so for 1', can only attack from 1 direction as only 1 sp2 pairs of electrons are delocalised 2'- 2 stabilising effect 3'- 3 stabilising effect on carbocation p orbital |
| What mechanism will a methyl X use? | SN2 If Halide only attached to Methyl, once halide is gone, there's nothing to stabilise the carbocation |
| What mechanism will a 3' use and why? | SN1 Once you lose halide, carbocation has stabilising effect from 3 groups of sp2 bonding not sn2 as the Nu: finds it physically hard to access the carbocation as the halide hasn't left a vacancy |
| What's the difference in reaction rate of the substitution reaction vs the elimination reaction? | Substitution - rate of reaction same whatever the nucleophile r=k[reactant] Elimination - rate of reaction is dependant on [reactant] and [OH-] r=k[reactant][OH-] |
| Describe E1 | Halide leaves, carbocation formed Nucleophile attacks a hydrogen, not the carbon centre Nucleophile removes hydrogens, the electrons from that bond move to form a double bond r=k[RX] |
| Describe E2 | All done in one step simultaneously r=k[RX][Nu-] |
| Draw a diagram of the E2 reaction | H electrons displaced into p bond of carbons as it's attracted to OH- X leaves |
| How do you determine whether a reaction is going to be substitution or elimination? | Depends on the strength of the base Strong base will attack H weak base will attack X, as it's going to want to donate its electrons to something already with a bit of a charge |
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