Topic 10- Halogenoalkanes Flashcards
What are the three classifications of halogenoalkanes and describe their positions?
What type of isomers are these?
What does the boiling point of halogenoalkanes increase with and why?
What does boiling point also increase for?
What does greater branching equal?
What is an example equation for the making of halogenoalkanes?
What is the name of the mechanism for the making of halogenoalkanes?
What are the three stages of making halogenoalkanes called?
- Primary 1o (end of the chain)
- Secondary 2o (in the middle)
- Tertiary 3o (at a branch)
Positional isomers
Increases with molecular size due to increased van der Waals’ forces between molecules
Also increases for straight chain isomers
Greater branching = lower inter-molecular forces
CH4 (g) + CL2 (g) —> CH3CL (g) + HCL (g)
Free-radical substitution
- Initiation
- Propagation (and substitution)
- Termination.
What is an example equation for the making of halogenoalkanes?
What is the equation for initiation?
What does the chlorine molecule do?
How does the Cl-Cl bond break?
What does initiation form?
CH4 (g) + Cl2 (g) —> CH3Cl (g) + HCl (g)
Cl2 —> Cl * + Cl *
Cl2 molecule absorbs one quanta of UV light
Cl-Cl bond breaks homolytically (homolytic fission of covalent bonds)
Forms Cl * free radicals.
What is the equation for initiation for the making of halogenoalkanes?
What does the chlorine molecule do?
How does the CL-CL bond break?
What is this called?
What does initiation form?
CL2 —> CL* + CL*
Cl2 molecule absorbs one quanta of UV light
CL-CL bond breaks homolytically
Homolytic fission of covalent bonds
Forms CL* free radicals.
What is the first equation for propagation in the making of halogenoalkanes?
What is the second equation for propagation?
What two products does propagation produce?
CL* + CH4 —> HCL + *CH3
CH3 + CL2 —> CH3CL + CL
Produces CL* and *CH3 free radicals.
What occurs in termination in the making of halogenoalkanes?
What is the first equation for termination?
What is the second equation for termination?
What is the third equation for termination?
What do two free radicals react to form in termination?
The free radicals are removed
CL* + CL* —> CL2
*CH3 + *CH3 —> C2H6
CL* + *CH3 —> CH3CL
In termination, two free-radicals react to form stable compounds with no unpaired electrons.
What is the definition of a halogenoalkane?
What are halogens generally much more than carbon?
What are most carbon-halogen bonds?
What does a halogen atom more than compared to carbon and so what does it do to carbon?
What does this leave the carbon atom as?
What does this leave the halogen atom as?
What does the f+ carbon not have enough of?
What does this mean it can be attacked by?
An with at least one halogen atom in place of a hydrogen atom
Halogens are generally much more electronegative than carbon
Most carbon-halogen bonds are polar
The halogen atom is more electronegative than the carbon atom and so withdraws electron density from the carbon atom
This leaves the carbon atom with a partial positive charge
This leaves the halogen atom with a partial negative charge
The f+ carbon doesn’t have enough electrons
This means it can be attacked by a nucleophile.
What is a nucleophile?
What is the function of a nucleophile?
What are three examples of nucleophiles that will react with halogenoalkanes?
A nucleophile is an electron-pair donor
It donates an electron pair to somewhere without enough electrons
Cyanide ion; ammonia; hydroxide ion.
What is the definition of nucleophilic substitution?
A reaction where one functional group is substituted for another.
What three things happen in a nucleophilic substitution reaction?
A nucleophile attacks a polar molecule, kicks out a functional group and settles itself down in its place.
What is the general equation for the nucleophilic substitution of a halogenoalkane?
What does the X stand for?
What does the Nu- stand for?
What is the carbon-halogen bond and so what is drawn?
CH3 CH2 X + (Nu-) —> CH3 CH2 Nu + (X-)
The X stands for one of the halogens
The Nu- stands for a nucleophile
The carbon-halogen bond is polar, so there are f- and f+ signs drawn on the molecule to represent the charges.
