CHEM 2 - Haloalkanes, mechanisms

Prefixes - -fluoro, -chloro, -bromo and -iodo indicate a halogen is present in the molecule. (Written in alphabetical order)

•  C-X bond (where X is a halogen) is polar, halogen is more electronegative than carbon, partial charges on C and X
• C-X bond not polar enough to be soluble in water
• Boiling point increases with chain length and halogen. Down the group halogen have greater vdW
• Haloalkanes have higher boiling points than their alkane counterparts due to higher RAM and polar bonds
• C in C-X bond is electron deficient and so can be attacked by electron-rich reagents
• These electron-rich reagents are called nucleophiles. They are electron donors
• Reactivity of C-X bond increases down the group

Nucleophiles are electron-rich reagents that attack partially positive carbon atoms

• Nucleophile can either be a negatively charged (partial or full) atom or charged atom within a complex ion
• C-X bond is always the bond which is broken. Stronger bond = slower reaction, C-F bond the strongest 
• In terms of reactivity, bond strength is more important than polarity. So even though C-F bond is the most polar, it is the least reactive

• Nucleophile approaches the delta+ carbon's backside and ends up forming a bond with it.
• Simultaneously the electron pair in the C-X bond gets pushed towards the X and the X comes of as a -ve ion, X-

SN2  - Subsitution, Nucleophillic, 2 species involved 

Conditions:

• Aqueous nucleophile-containing reagent
• Dissolved in ethanol (since haloalkane is insoluble in water, hydrolysis reaction)
• Water encourages substitution
• Room Temp

OH- acts as a base removing a H

 Conditions:

• Elimination favours:
• Heat
• Pure ethanol, no water
• Concentrated KOH/NaOH