#nucleophiles

Ionic Reactions

Nucleophilic Substitution and Elimination of Alkyl Halides

 Alkyl halides – has a halogen atom (Br, Cl, F, I) bonded to an sp3-hybridized (tetrahedral) carbon atom.

-          The C-H bond is a polar bond. This is because the halogen atom hogs the electrons towards its side due to its electronegativity trait (it is more electronegative than carbon). This results to the carbon having a δ+ (partially positive charge) and the halogen a δ- (partially negative charge).

-          Can be classified as primary, secondary, or tertiary:

o   Primary (10) – has one R group (carbon group) directly bonded to the carbon bearing the halogen atom.

o   Secondary (20) – has two R groups directly bonded to the carbon bearing the halogen atom.

o   Tertiary (30) – has three R groups directly bonded to the carbon bearing the halogen atom.

-          As the halogen atom decreases in size, the C-X (X=halogen) bond decreases and the bond strength increases, and the polarity increases. (Therefore C-F is most polar and has the strongest C-X bond and C-I is the least polar and has the weakest C-X bond)

 Alkenyl halides – a compound in which the halogen atom is bonded to an alkene

Aryl halides – a compound in which a halogen atom is bonded to an aromatic ring

-          Phenyl halides – if the aromatic ring is a benzene ring

 Physical Properties of Alkyl Halides

1.       Most alkyl halides have very low solubilities in water and other polar solvents.

2.       Miscible with each other and other relatively nonpolar solvents.

3.       Many chloroalkanes have cumulative toxicity and are carcinogenic.

 Nucleophilic Substitution Reactions

-          Among the most fundamental types of organic reactions.

-          A nucleophile (Nu:) displaces a leaving group (LG) in the molecule that undergoes the substitution (substrate).

o   Nucleophile – always a Lewis base, may be negatively charged or neutral.

o   Leaving group – always a species that takes a pair of electrons with it when it departs.

-          Often, substrate – alkyl halide (R-X) and the leaving group – (X-).

-          Nu-         +             R – LG                   →                           R – Nu                   +             LG-

 Nucleophiles – reagent that seeks a positive center

-          Any negative ion or uncharged molecule with an unshared electron pair.

1)      Negatively-charged nucleophile – results in a neutral product. Formation of the covalent bond between the negative nucleophile and the substrate neutralizes the formal charge of the nucleophile

o   H-O-               +             R-X         →                           H-O-R                    +             X-

2)      Neutral nucleophile – results initially in a positively-charged product.

o   H2-O-                     +             R-X         →                           H2O-R                    +             X-

NUCLEOPHILIC SUBSTITUTION.

That just does it for me. Isn't that just the most awesome name for something ever?

A nucleophile is an ion or group of atoms with a negatively charged area or partially negatively charged area that takes part in an organic reaction by... listen to this ATTACKING AN ELECTRON DEFICENT AREA IN ANOTHER REACTANT :o

Isn't that like shocking? *The feels for that poor atom*

  These attacks are called NUCLEOPHILIC SUBSTITUTIONS.

  And they can be illustrated like so...

*

-The CURLY ARROWS (that is actually their technical name- whoever came up with this is also awesome) represent how the nucleophile is attracted to the slightly positive charge of the carbon atom.

  -The electron pair is donated to X to create the halogen ion which is called a leaving group :'( how very emotional *sniff* just take a closer look at him he's like a cross face with a tear if you turn him on his side-->

(That is how you should remember to draw him, in that really emotional way)

So basically in this reaction the poor old halogen ion is kicked out and replaced by this nasty nucleophile.

  Some examples of nasty nuclophiles are:

:o

      *One girl in my chemistry class who I'm not particularly a fan of just burst out "OMG NO WAY IS THE SYMBOL FOR A NUCLEOPHILE THAT! IT'S THE SAME SYMBOL ON MY BOOK! NOW I KNOW WHAT IT MEANS"... And everyone was laughed at her and was like, no, that's the name of a company who supply asda, I doubt they took the inspiration from chemistry.

Does anyone know those notebooks you get? They look like this-->

  And then she was just sighed and went "ohh I thought I'd finally figured something out, anyway the dots are the wrong way round"