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Organic & Biomolecular Chemistry, Reduction of aldehydes and ketones -…
Organic & Biomolecular Chemistry
Atoms, Elements and Compounds
Atom make up all matter
Sub-atomic particles
An atom is composed of positively charged nucleus (protons) , negatively charged electrons and neturons.
Electrons are orbiting the nucleus. The closer the layer to the nucleus, the stronger that attraction and the lower the electron energy.
Electron arrangement: Rows in periodic table rep #of layers
Valence electron at the outermost layer is where chemical reactions occur.
Group number in periodic table = number of valence electrons
Ionisation Energy- amt of energy to remove an electron completely from atoms
Electronegativity is a measure of an atom's ability to attract shared electrons to itself.
compounds are represented using chemical formulas
(Symbol of elements = subscripts )
Chemical Bonds
Ionic bond :complete transfer of electrons from on to the other elements( metal and non meta)
Covalent bond: elements share electron ( non mental atoms)
Polarity and EN
EN difference < 0.5, non polar
EN difference ≥ 0.5 , polar
EN difference > 2 , ionic bond
Non polar covalent when both atoms share electrons equally
Polar covalent when both atoms do not share electrons equally
Intro to Organic chem
Molecular Formula
eg. Formula: C3H6O
Structural Formula
IUPAC
Ranking in Functional Group
Name the functional group using the “As suffix in parent” column when it is the highest ranked functional group in the molecule
Otherwise, use the given names in the “As Substituent” column
Any other functional group not mentioned in table, e.g. halogen (Group 7) is always treated as substituent
How to name nomenclature
1.Locate and rank all functional groups
2.Locate unsaturations (double or triple bond)
3.Locate main/parent chain
it must include all functional groups and all unsaturation
It must be contain as much Carbon atoms as possible
4.Number the main/parent chain
5.Start naming the Parent Chain
6.Start naming the various substituents and note their positions
Hydrocarbon
Contains Carbon + Hydrogen
saturated bonds - Alkanes
unsaturated - Alkenes & Alkynes
Alkanes ( C-C )
general formula:CnH2n+2
Alkenes ( C=C )
general formula:CnH2n
Alkynes ( C≡C )
general formula:CnH2n-2
Properties :
non-polar
insoluble in water
The stronger the dispersion force, the higher the boiling or melting point.
Isomerism in Hydrocarbons
Structural isomers have same number of atoms, but different arrangement
Compounds that have same molecular and structural formulas but a different spatial arrangement of atoms or groups because of restricted rotation about double bond or ring system
*( only alkenes ) cis -same side , trans- opposite side
Rections
Elimination reaction
Dehydrohalogenation
Use of base to remove acidic H-X elements (HCl, HBr, HI) from alkyl halide . Solvent -Alcohol/water
Dehydration
Water removed from adjacent carbons of alcohol
For assymetrical alkane reactants => Most stable product is the one which has more no. of substituents or R-groups attached to the double bond (Zaitsev’s rule)
Addition reaction
1.Hydrogenation (add H2)
Reaction condition: Increase temperature/pressure Catalyst like Pt, Pd or Ni
2.Hydration( add H2O)
Condition: requires acid & formation of an alcohol
*follows Markovnikov’s rule
3.Hydrohalogenation (add acid halide)
forms alkyl halide
*follows Markovnikov’s rule
4.Halogenation ( add halogen gas Cl2 &Br2)
formation of alkyl halide
Substitution reaction
Substitution of Alkane: Halogenation
CH4 + Cl2 + energy —> CH3Cl + HCl
Energy - form of heat or light to initiate these halogenations
*Halogenation are more likely to occur for secondary or tertiary hydrogens
Aromatics
Benzene
Aromatic-Nomenclature
~Simple compounds are named as substituted benzene derivatives
~Commercial/ Common Names
If there are 2 substituents,
Reactions of Aromatics
Aromatic Substitution: one or more H atoms on the ring can be substituted by other functional group
:star:Halogenation -Catalyst=Lewis Acid Catalyst
:star:Alkylation- Alkyl group from chloroalkane substitutes H atom on the ring
-Catalyst=FeX3
R= alkyl/hydrocarbon group
-An important step in alkyl benzene synthesis
:star:Nitration: -catalyst= Concentrated Nitric Acid(conc.H2SO4)
:star:Sulphonation:-Substitution with sulphonic acid group
Substitution-Orientation
Predict orientation: -The initial presence of one substituent on an aromatic ring will dictate the position of the second substituent added to the ring during a reaction.
-2types of directing effect ~ Ortho/Para director= Second group go to either ortho or para position
~Meta director= Second group go to meta position
:star:Oxidation: - Alkyl group of alkyl benzenes can be easily oxidized by acidified KMnO4 ( strong oxidizing agent) to carboxylic acids
-All primary and secondary groups are oxidized to COOH regardless of size
-Tertiary alkyl groups are oxidized into phenols
Aldehyde and Ketone
Aldehyde
C=O bond at the end
R is a hydrocarbon chain group
Ketone
C=O not the end
R is a hydrocarbon chain group
Preparation:
:star:Hydration of alkynes~Catalyst=H2SO4 & HgSO4
:star:Ozonolysis of alkenes~ Replacement of C=C bond with C=O bonds which result in 2 carbonyl products from 1 alkene
~Catalyst=O3,Zn & H2O
:star:Friedel-Crafts Reaction (Acylation with Acid Chloride)
~Catalyst=AlCl3 or FeCl3
:star: Oxidation of alcohols~Catalyst= Mild oxidizing agent(PCC) or strong oxidizing agent (for complete reaction in primary alcohol)
~Aldehydes can be further oxidized to carboxylic acids(Oxidation Reaction)
Reactions
:star:Tollens's Test:~ Can be used to distinguish between aldehydes and ketones by using Tollens's reagent
~Silver ion is reduced to metallic silver that gives a mirror effect on the test tube wall
~Aldehyde gives a positive result
~Ketone gives a negative result
:star:Reduction Reactions:~Conversion to alcohols
~H2 addition reaction
~Aldehydes result in primary alcohols
~Ketones form secondary alcohols
~Catalyst=Pt/Pd/Ni
:star:Nucleophilic Addition Reactions due to +dipole on C):~Addition of H2O-Catalyst=H+
~Addition of ROH-Catalyst=H+
~Addition of Grignard Reagent(R-MgX+)
Carboxylic Acid
Carboxylic acid derivatives have the general formula:
-Z=chloride/NH2/alkoxy/anhydride
Acid chloride
~Naming same as acid but replace -oic acid with -oyl chloride
Amide
~Naming similar to carboxylic acid-drop the -oic acid ending and replace with -amide
Amide Preparation :star:Least reactive of the series, can be prepared by reaction of ammonia with acid chlorides, acid anhydrides, carboxylic acids, & esters.
:star:Production from Carboxylic Acids-Catalyst=NH3& Heat
:star:Production from an acid chloride-Catalyst=NH3 & Heat
Acid Anhydride
~For symmetrical anhydrides.name by changing acid ending to anhydride
~For asymmetrical anhydrides, name n=both halves separately
Acid Anhydride Formation
:star:Conversion from less reaction to a more reactive (acid anhydride)-Catalyst= H+ & heat
:star:Reverse process (hydrolysis of acid anhydride) spontaneously occur only by heat-Catalyst=Heat
Ester
~OH of acid replaced with
-OR group-Name R group like a side chain
-Name acid portion with -oate ending
Ester Formation
:star:Dehydration:-Reaction carried out with acid catalyst
-Another ester will form when further react with a different alcohol~ exchange of R groups(trans-esterification)
Preparation: :star:Oxidation of primary alcohols/aldehydes-Catalyst=mild/strong oxidising agent
:star:Primary and secondary alkyl group of alkyl benzenes can be oxidized to carboxylic acids which required acidified & strong KMnO4 &H2SO4
Alkyl
Halides
Reactions
Hydrohalogenation(Alkyl halide preparation)
Aromatic substitution
Reaction between benzene and halogen gas
:star: Required Catalyst: Lewis acid ,with same identity as halogen gas
Nucleophilic substitution
Replacement or substitution of halide group with nucleophiles
:star:
Halogenation(Alkyl Halide preparation)
-Halogen replaces one or more hydrogen atoms through free radical substitution
-Conditions=Heat & Under UV light
Alcohols
Preparation
Hydration:Addition of water to an alkene
:star: Small amount of acid needed
:star:Nucleophilic substitution of alkyl halides
Derivatives
:star: Ethers: Contain 2 alkyl or aryl (aromatic ring) groups bound to an oxygen
:star: Phenol: A benzene (aryl) with an alcohol group attached to it
:star: Thiols: Similar to alcohol but have sulphur instead of an oxygen
Reactions
:star: Dehydration:-Removal of water to form an alkene
-Catalyst-Concentrated acid and heat
:star: Oxidation of alcohols: breaking of C-H bond to form new C-O bond~Conversion of OH to C=O(carbonyl)
-Oxidation happens at C connected to the OH in alcohols
-Starting alcohol must have at least 1 C-H bond~Tertiary alcohols cannot be oxidized
-Primary alcohols(2H) can be oxidized twice (first to aldehyde then to carboxylic acid)
-Catalyst=mild oxidizing agent (get aldehydes)/strong oxidizing agent (get carboxylic acid at one time)
Amine
Preparation
:star:Reduction of Nitriles: Reactions that introduced chemical bonds with hydrogens
-Catalyst=Ni/Pt/Pd
:star: Alkylation of Amines: Amine are nucleophiles
Chromophore group
:star: Nitro
:star: Azo
Reduction of aldehydes and ketones
:star: Catalytic Hydrogenation
-Breaking C=O in aldehyde/ketone
-Hydrogen atom add to both C and O to form alcohol
:star: Grignard synthesis
-Grignard reagents are nucleophiles(electron rich)
-C=O bond are polarized with partial positive charge on C
-Catalyst= H2O/H+
