Organic Reactions. Point #1 3 basic kinds of reactions A) Addition Reactions (like synthesis...
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Transcript of Organic Reactions. Point #1 3 basic kinds of reactions A) Addition Reactions (like synthesis...
Organic Reactions
Point #13 basic kinds of reactions
A) Addition Reactions (like synthesis reactions)• Hydrogenation
– saturating an unsaturated carbon chain– alkene/yne to alkane
• Hydration– alkene to alcohol
• Halogenation/Hydrohalogenation– alkane to haloalkane– alkene to haloalkane
B) Elimination Reactions (like synthesis reactions because they result in larger compounds)
• Condensation– Esterification– Formation of alkene– Formation of amide (peptide bond)
C) Substitution Reactions (like single or double replacement reactions where one atom/ion/functional group is replaced by another)
• SN1
• SN2
Point #2 Basic process of organic reactions is through attraction of
positively (electrophile) and negatively (nucleophile) charged parts of
molecules
Electrophiles Nucleophiles “loves electrons” =
attracted to negative charge
“loves nuclei” = attracted to positive charge
maybe positively charged or have deficit of electrons b/c atom is attached to very electronegative atom
often negatively charged or
lone pairs high electronegativity
carbon of carbonyl group acids
alkenes Hydroxide –OH Chloride –Cl Ammonia – NH3
– many organic reactions happen through the attraction of electrophiles for nucleophiles
– in reaction mechanisms, curly arrows show how electrons move – generally electrons from nucleophile move to electrophile
Point #3 Alkanes/Alkenes are relatively inert compared to other functional
groups A) Alkenes have pi bonds in which electrons are
easily accessible b/c they aren’t trapped between two nuclei as sigma bonding electrons are.
B) Other functional groups have highly electronegative atoms like O, N or halogens
The table below gives the characteristic reactions for several functional groups
Functional Group
Addition Elimination Substitution
Alkane Halogenation (haloalkanes)
Alkene Hydrohalogenation (mono-haloalkanes,)
Hydration (alcohols)
Halogenation (di-haloalkanes)
Hydrogenation (alkanes)
Oxidation (-OH, C=O, COOH)
Alcohol Condensation w/ COOH to (ester)w/ conc. acid or catalyst (alkene)
Oxidation (aldehyde, ketone, COOH)
Carboxylic Acid Condensation with –OH (ester)
Amine Condensation w/ COOH (amide)
ReactionsExample #1-Halogenation of alkane
– Alkane + halogen gas haloalkane– Need ultraviolet light for rxn to occur– Depending on time and amount of reactants,
more than one halogen can added to the alkane
H
H
H
H+ Cl Cl
hCl
HH
HClCl
H
HClCl
H
Cl
ClCl
Cl
Clchloromethane dichloromethane chloroform tetrachloromethanemethane
also: trichloromethane also: carbontetrachloride
h h h
• Free radical is a element or molecule with an unpaired electron
• Homolytic fission vs Heterolytic fission:
– Fission means splitting apart
– Heterolytic means that one atom takes both electrons in the bond and two ions are formed.
– Homolytic means the bond is split in half – each side takes 1 electron and 2 free radicals are formed
-Reaction occurs through homolytic fission to form a free radical
Formation of free radicals often results in chain reactions –
reaction keeps occurring until all reactant is used up. See
polymerization notes form mechanism.
Example #2-Hydrohalogenation
– Alkene + acid halide monohaloalkane
– Halide ion adds to larger side (more substituted side of alkene) if there is one
H
H H
H
+HH
H
HH
ClH Cl
Hydrohalogenation of ethene
Hydrohalogenation of 1-propene
H
H CH3
H
+CH3
H
H
HH
ClH Cl
H Cl+ C+
CH3H
H
H H
+ Cl-
CH3
Cl
H
H
H H
CH3H
H H
Example #3-Hydration
– Alkene + water in acidic solution alcohol
– Acid acts as catalyst in rxn– –OH group adds to larger
side (more substituted side) of alkene
– Uses: hydration is used for commercial manufacture of ethanol
Hydration of etheneH
H H
H
+ OHH
a c idO
H
H
H H
H
H
Hydration of 1-propeneH
H CH3
H
+ OHH
a c id
CH3
O
H
HH
H
H
Example #4 -Halogenation
– Alkene + halogen gas 1,2-dihaloalkane– Diatomic gas has two atoms – both add to opposite sides
of the double bond (and opposite sides of the molecule)– Uses: Chlorine + ethane 1,2-dichloroethane: used as
starting material for PVC– Uses: Br2 dissolved in dichloromethane is used to
distinguish between alkenes and alkanes. If reddish-brown color of Br2 disappears when added to unknown, the unknown has alkenes in it.H
H H
H
+HH
Cl
HH
ClCl Cl
Example #5 Hydrogenation
– Alkene + Hydrogen gas (with catalyst) alkane– Hydrogenation is saturating an unsaturated hydrocarbon – Addition Reaction– Heterogeneous Catalyst: Pd or PtO2 (rxn occurs on a metal
surface)– Uses: unsaturated vegetable oils are saturated to produce
saturated fats (more solid at room temp than unsaturated) for margarines
H
H H
H
+HH
H
HH
HH H
P tO 2 /P d
Example #6 Esterification– Carboxylic acid + alcohol ester + water– Reaction conditions: acidic solution– The OH group on the carboxylic acid is replaced by the alcohols
O-R group– Condensation reaction: produces water– Uses: flavouring agents, plasticizers, as solvents in perfume,
polyesters
OH
O+ OH
O
Oac id
acetic acid propan-1-ol ethyl acetate
OH
O
OH O
O
propionic acid
propan-1-olpropyl propionate
+a c id
+
+
OH2
OH2
Examples #7 Amide formation
– Carboxylic acid + amine amide + water – Reaction condition: difficult to conduct in simple steps– The OH group on the carboxylic acid is replaced by the amine (NH-R)– Condensation rxn: produces water– Uses: peptide bond formation, polymerization reactions to make
nylons
H3C OH
ONH2 CH3+
O
H3C NHCH3acetic acid methanamine
N-methylacetamidealso: ethanoic acid
OH
ONHCH3
CH3+
O
NCH3
CH3
N-methylmethanaminebutyric acid
N,N-dimethylbutanamidealso: butanoic acid
Example #8 Oxidation of alcohol
– Alcohol + oxidizing agent COOH (1, complete) /Aldehyde (1, partial)/Ketone (2)
– Obviously an Oxidation reaction
– Reaction condition: aqueous, acidic solution. The carboxylic acid and the aldehyde can be obtained through different experimental set-ups
• Distill to get aldehyde• Heat under reflux to get COOH
Oxidation of alcohol (continued)
– Complete Oxidation: primary alcohol + oxidizing agent carboxylic acid
+OHa c id
K 2C r 2O 7
O
OHpropan-1-olpropanoic acid
Oxidation of alcohol (continued)
• Partial Oxidation: primary alcohol + oxidizing agent aldehyde
+OHa c id
K 2C r 2O 7
O
Hpropan-1-ol1-propanal
Oxidation of alcohol (continued)
• Secondary alcohol + oxidizing agent ketone
+OHa c id
K 2C r 2O 7
O
butan-2-ol butan-2-one
Example #9 Condensation of alcohol
– Condensation of alcohol alkene– Reaction conditions:
• 170 and concentrated sulfuric acid or• H3PO4 and a catalyst or Al2O3 and a catalyst
H3C
CH
H3C
OHC
C
H3C
OH
H
HHH
HO
H
CH2
CHH3C