20994307-CH6 - CHAPTER 6 Properties and Reactions of...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
CHAPTER 6 Properties and Reactions of Haloalkanes: Bimolecular Nucleophilic Substitution
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Physical Properties of Haloalkanes 6-1 The bond strength of C-X decreases as the size of X increases. A halogen uses a p orbital to overlap an sp 2 orbital on a carbon atom. As the size of the halogen p orbital increases (F < Cl < Br < I), the percentage overlap with the smaller sp 2 carbon orbital is less and the bond strength decreases.
Background image of page 2
The C-X bond is polarized. Because halogens are more electronegative that carbon, carbon- halogen bonds are polarized. The halogen atom possesses a partial negative ( δ - ) and the carbon atom a partial positive ( δ + ) charge. The electrophilic δ + carbon atom is subject to attack by anions and other nucleophilic species. Cations and other electron-deficient species attack the halogen atom.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Haloalkanes have higher boiling points than the corresponding alkanes. Boiling points of haloalkanes are higher than those of the parent alkanes mainly due to dipole-dipole interactions between the haloalkane molecules: As the size of the halogen increases there are also larger London forces between the haloalkane molecules. Larger atoms are more polarizable and interact more strongly through London forces.
Background image of page 4
Nucleophilic Substitution 6-2 Haloalkanes can react with nucleophiles at their electrophilic carbon atom. The mucleophile can be charged, as in :OH - or neutral, as in :NH 3 . In nucleophilic substitution of haloalkanes, the nucleophile replaces the halogen atom.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Nucleophilic Substitution 6-2 Nucleophiles attack electrophillic centers. Nucleophilic substitution of a haloalkane can be described by two general equations: In both cases, the leaving group is the halide anion, X - . In describing reactions, the organic starting material is called the substrate of the reaction. Here, the substrate is being attacked by a nucleophile.
Background image of page 6
Nucleophililc substitution exhibits considerable diversity. Rxn 1: OH - (KOH) displaces Cl - to produce an alcohol. Rxn 2: OCH 3 - displaces Cl - to produce an ether. Rxn 3: I - displaces Cl - to produce a different haloalkane. Rxn 4: CN - (NaCN) displaces Cl - to form a new C-C bond.
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Rxn 5: The S analog of Rxn 2 forming a thioether. Rxn 6: Neutral :NH 3 produces a cationic ammonium salt Rxn 7: Neutral :PH 3 produces a cationic phosphonium salt.
Background image of page 8
Halides can serve as nucleophiles and as leaving groups in nucleophilic substitution reactions. These reactions are reversible. Strong bases, such as HO - and CH 3 O - , however do not serve as good leaving groups. Substitution reactions involving these species are not reversible.
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Reaction Mechanisms Involving Polar Functional Groups: Using “Electron-Pushing” Arrows 6-3 Curved arrows depict the movement of electrons. The oxygen lone pair of electrons ends up being shared between the oxygen and the hydrogen.
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/04/2009 for the course CHEM 120 taught by Professor Johnmichael during the Spring '09 term at Tennessee Martin.

Page1 / 48

20994307-CH6 - CHAPTER 6 Properties and Reactions of...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online