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alkyl halides or haloalkane
an alkane connected to a halogen
aryl halides
an aromatic ring connected to a halogen
vinyl halides
an alkene connected to a halogen
for alkyl halides, the bond length _________ as a ______ atomic mass atom is attached to the molecule.
increases, higher
for alkyl halides, the most polar molecule is attached to a ______ electronegative atom.
higher
Radian Chain Mechanism (3)
Initiation, Propagation, and Termination
Initiation
With some light or heat, the bond btwn Cl2 breaks and is split homolytically to produce 2 radicals (atoms or molecules w/ unpaired e-.
Propagation
In 2 propagations steps, a radical combines with a neutral molecule to make a new radical and a new neutral molecule.
What happens in the 1st propagation step?
In the first step, the halogen radical combines with a neutral alkane to make a new radical and neutral molecule.
What happens in the 2nd propagation step?
In the 2nd step, the bond of the halogen gas are broken. One halogen atom becomes a radical and the other combines with the radical alkane.
Termination
Two radicals come tgt to form a neutral cmp, forming more product, reactant, and side product.
Of the three steps of radical chain mechanism, the slowest or rate-determining step is….
propagation
In order to get monosubstituted chloromethane, one way is…
use a higher concentration of alkane in comparison to chlorine
What is the main path for halogenation? In other words, what position do halogens selectively substitute more? Why?
the secondary carbon because more substituted radicals are, the more stable
Who is more selective? Chlorination or bromination?
bromination
What is substitution reaction of alkyl halides?
A good nucleophile bonds with a alkyl halide creating a neutral cmp. and an anion.
What is elimination reaction of alkyl halides?
A base bonds with an alkyl halide and creates a neutral cmp. and an anion
What are two reasons that alkyl halides undergo substitution and elimination?
1) Halogen is susceptible to nucleophilic attack due to its ability as an electron withdrawing group.
2) Halogen acts as a GOOD leaving group.
What does substitution require?
1) loss of a leaving group
2) nucleophilic attack
What are the 2 possible substitution mechanism?
SN2 and SN1
What happens in SN2 or bimolecular nucleophilic substitution reaction?
A one-step mechanism involves breaking the bond of the leaving group and the making of the bond to the nucleophile happening at the SAME time.
What happens in SN1 or unimolecular nucleophilic substitution reaction?
A multi-step mechanism involves the leaving group leaves and a carbocation forms, which subsequently forms a bond with the nucleophile.
What is the transition state structure? What reaction is it part of?
The nucleophile transfer e- to the C atom and becomes partially negative. The higher electronegative atom or the leaving group will gain an e- and become partially negative.
Why does the nucleophile attack from the back-side?
1) Front-side is e- dense.
2) Homo of nucleophile can flow to the lumo of the electrophile.
What happens to the chiral carbon of the SN2?
Since the reaction is stereospecific, the alpha carbon (reaction site) will undergo an inversion of configuration.
What prevents SN2 from happening? What does that mean?
Too much steric hinderince meaning more branching on the alpha and beta carbons of alkyl groups results to a lower rate of rct.
What determines or influences the strength of the nucleophile?
1) charge
2) resonance
3) electronegativity
4) atomic mass
5) steric hinderance
What makes a strong nucleophile?
1) anion
2) no resonance
3) low electronegativity
4) bigger atomic mass
5) less hindered
What is the PT pattern for a strong nucleophilicity?
Right to Left and Top to Bottom
What are the 8 strong nucleophiles?
chloride ion (Cl-), bromide ion (Br-), iodide ion (I-), HS-, RS-, HO-, RO-, and N(triple bonded)C-
What are the 4 polar aprotic solvent?
DMF (O(double bonded)C(bonded to)H and N(bonded to) R1 and R2, DMS (sulfide), DMSO (O(double bonded)S(bonded to)R1 and R2, and acetone (ketone)
How can you identify a protic solvent?
1) solvent that can donate protons
2) Does it have a OH or NH?
What is the requirements of a SN2 reaction?
strong, big nucleophile and polar aprotic solvent
What is the rate-determining step in a SN1 reaction?
carbocation intermediate
What is the relationship btwn the carbocation intermediate and the rate of SN1?
directly proportional, so the more stable the carbocation intermediate, the faster the reaction
