CnH2n+1X X is more e- than C so it pulls the electrons in the bond closer to itself, gaining a partially negative charge, making the carbon it is bonded to partially positive (or electron deficient)
1. BEILSTEIN TEST •
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General Test for halides Produces green colored flame except F2 which is non-volatile
mrsantiago(Chem 200 lab, AY 2014-2015)
NUCLEOPHILIC SUBSTITUTION (SN) •
•
One covalent bond is broken as a new covalent bond is formed The general form for the reaction is Nu:- + R-X
Nucleophile +
haloalkane
R-Nu +
X:-
Substituted Product + Leaving group/halide
What is a NUCLEOPHILE? •
•
A nucleophile is a molecule or ion that has a high electron density, so its attracted to atoms in molecules with a lower electron density. It may replace another group in an organic molecule. –
–
They are attracted to the electron deficient carbon in the haloalkane Typical nucleophiles: H2O, OH-, NH3, CN-
NUCLEOPHILIC SUBSTITUTION UNIMOLECULAR (SN1)
2-Step reaction: 1. Dissociation of RX to C+ and X2. Attachment of Nu- to R+ Reactivity is based on stability of C+ •
•
•
Rate of reaction is dependent on RX
SN1 REACTION •
Order of reactivity is affected by nature of alkyl halide –
Leaving group (more electronegative, better leaving group) F > Cl > Br > I > OH > NH 2
Reactivity is dependent on the steric effect of the rear end of the functional C
•
•
Rate of reaction is dependent on RX and Nu-
SN2 REACTION •
Order of reactivity is affected by: –
Degree of branching (steric hindrance) 10 > 20 > 30
–
Strength of nucleophile -NH2 > -OH >
Summary (Expt 8) SAMPLE
BEILSTEIN TEST
Ethanolic AgNO3 (SN1)
NaI in acetone (SN2)
Green flame
(3)+++
(1)+
Green flame
(2)++
(2)++
Green flame
(1)+
(3)+++
Green flame
(4) +/-
NR (-)
HYDROXYL CONTAINING HYDROCARBON DERIVATIVES
mrsantiago(Chem 200 lab, AY 2014-2015)
SOLUBILITY OF ALCOHOLS IN WATER •
Polar hydroxyl group
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Non-polar/hydrophobic hydrocarbon chain
•
#C, hydrophobic, polar, soluble in H2O
•
branched, hydrophobic, soluble in H2O
Solubility in water:
30 > 20 > 10
mrsantiago(Chem 200 lab, AY 2014-2015)
Lucas Test (SN1) •
Substrates that easily give rise to cationic character at the carbon bearing the hydroxyl group undergo the Lucas test readily.
Alkyl halide appears as a second liquid layer + Test: Formation of insoluble layer or emulsion in 5-10 min N o t e : Primary alcohols do not give positive result.
mrsantiago(Chem 200 lab, AY 2014-2015)
CARBONYL CONTAINING HYDROCARBON DERIVATIVES
mrsantiago(Chem 200 lab, AY 2014-2015)
OXIDATION OF ALCOHOLS AND ALDEHYDES
No rxn
No rxn mrsantiago(Chem 200 lab, AY 2014-2015)
Oxidation tests 1. Jones or Chromic acid test 2. Tollens or Silver mirror test 3. Fehling’s test
mrsantiago(Chem 200 lab, AY 2014-2015)
CHROMIC ACID TEST (JONES OXIDATION TEST) •
Differentiating test for oxidizable carbons
No Reaction
TOLLEN’S (SILVER MIRROR) TEST •
Test for oxidizable carbon
•
Reduction of Ag+ to Ag
No rxn
FEHLING’S TEST
•
Test for oxidizable carbon –
•
Differentiating test for aliphatic(+) and aromatic (-) aldehydes
Components: –
Fehling’s A: CuSO4(aq)
–
Fehling’s B: potassium sodium tartrate, NaOH
No rxn
FEHLING’S TEST
2,4-DNPH TEST •
Test for presence of carbonyl group (aldehydes and sterically unhindered ketones) –
•
•
formation of hydrazone
Reagent: 2,4-dinitrophenyl hydrazine
Can be used to differentiate aromatic and aliphatic carbonyl containing organic compound – –
Aromatic: red orange ppt Aliphatic yellow orange ppt
