A level Chemistry Topic 17/18 - Organics II & III
Grignard + Carbon dioxide
(Form Grignard : CH₃CH₂Br + Mg → CH₃CH₂MgBr (ether)) 1) React by bubbling through dry CO₂ CH₃CH₂MgBr + CO₂ → CH₃CH₂COOMgBr 2) Hydrolysis with acid CH₃CH₂COOMgBr + H₂O →(H⁺)→ CH₃CH₂COOH + Mg(OH)Br
Grignard + Carbonyl Compounds
(form grignard) 1) Add grignard across double bond CH₃CH₂MgBr + CH₃COH → CH₃CH₂CH(CH₃)OMgBr 2) Acid Hydrolysis CH₃CH₂CH(CH₃)OMgBr + H₂O → H⁺→ CH₃CH₂CH(CH₃)OH + Mg(OH)Br
Benzene - Nitration
*reagent*: conc nitric and sulphuric acid *conditions* : warm + reflux 1) HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂O 2) * NO₂⁺ react via electrophilic substitution mechanism* 3) forms nitrobenzene and H⁺ + HSO₄⁻ → H₂SO₄
Organic Synthesis Techniques - Purity Test - melting temperature
- impurities decrease meting temperature of a compound as they disrupt intermolecular bonding, & ↑ range over which substance melts -place solid in small capillary tube attached to bulb of thermometer in liquid that has boiling point above solid -heat up and detect when melted
Trends in Basicity of ammonia, aliphatic and aromatic amines
- primary amines more basic than ammonia as alkyl groups are electron releasing ∴ ↑ electron density of nitrogen = ↑ ability to protonate -↑ HC chain length = ↑ electron releasing = ↑ basicity -phenylamine = lp on nitrogen donated to delocalised 𝜋 bond = ↓ ability to protonate = ↓ basic & less soluble in water
Organic Synthesis Techniques - refluxing
-Add a condenser to top of reaction mixture = prevent volatile reactants or products from evaporating and escaping -Add antidumping granules to prevent overbooking -water in bottom, out at top to cool condenser efficiently
Ester naming
-First word comes from alkyl group joined to O (becomes alcohol during hydrolysis) -Second word comes from alkyl group connected to C (becomes carboxylic acid ) -oate
carbonyl and cynaide
-HCN in situ (KCN + OH- under reflux at RTP) -nucleophilic addition -extend HC chain -can produce racemic mixture as CN attack from above or below Mechanism 1)CN- attack nucleophilic carbon 2)O:⁻ breaks H-CN to form OH + CN⁻ =hydroxynitrile
Grignard Reagent + synthesis
-Organometalli compounds containing magnesium -RMgX - dipole as carbon is δ-ve -acts as reducing agent and nucleophile Reagent: Halogenoalkanes + Magnesium Conditions : DRY (day ether) Heat with reflux under waterbath for approx 20 mins CH₃CH₂Br + Mg → CH₃CH₂MgBr
Acyl Chloride + Alcohols
-Reagent: Alcohols -Conditions: reflux in dry/anhydrous conditions -Product: ester + HCl -Observation: Misty fumes + ester/fruity smell -Equation:CH₃COCl + CH₃OH → H₃CCOOCH₃ + HCl
Acyl Chloride + Conc Ammonia
-Reagent: Ammonia (Conc) -Conditions: Low temp + excess ammonia -Product: Amide + HCl -Observation: white smoke -Equation: 1) CH₃COCl + NH₃ → CH₃CONH₂ + HCl 2) HCl + NH₃ → NH₄Cl OVERALL CH₃COCl + 2NH₃ → CH₃CONH₂ + NH₄Cl
Acyl Chloride + water
-Reagent: Water -Conditions: RTP -Product: Carboxylic Acid + HCL -Observation: Misty fumes due to HCl -Equation: CH₃COCl + H₂O → CH₃COOH + HCl
Acyl Chloride + Amine
-Reagent: amine (RNH₂/R₂NH) -Conditions: Anhydrous RTP -Product: N-Substituted Amide -Equation: a. Primary CH₃COCl + CH₃NH₂ → CH₃CO-NHCH₃ + HCL (N-methyl amide) b. secondary CH₃COCl + (CH₃)₂NH → CH₃CON(CH₃)₂ + HCl Does not work with 3° Amide as no H to make HCl
Phenol - properties
-benzene with hydroxyl attached -crystalline solid ∴ ↑ intermolecular forces compared to benzene (H-bond) -acts as a weak acid in water as ring helps to stabilise phenoxide anion and break OH C₆H₅OH ⇌ C₆H₅O⁻ + H⁺
Ester Physical Properties
-colourless liquids -insoluble in water, soluble in organics -No H-bonds as all hydrogen bonds attached to carbons -fruity smells
Formation of a polypeptide
-condensation polymerisation - form peptide bond and eliminate water
Amine - Functional group & properties
-consists of Nitrogen with 3lp and 1bp bound to alkyl groups and hydrogen -trigonal pyramidal shape -characteristic Rotting Fish Smell - Alkaline Solutions as can accept H⁺ -more soluble in acid than water as can accept H⁺ -sparingly soluble in water due to H-bond between NH & OH, ↑ HC chain = ↓ soluble
Benzene - Freidel Craft Reactions
-halogen carrier is used with haloalkane to react with benzene ring and add alkyl/acyl compounds. -must be done in dry conditions otherwise H₂O reacts with catalyst
Hydrolysis of a peptide
-heat for long time with conc HCL -forms protonated amino acid as acid hydrolysis dipeptide + H₂O + H⁺ = 2 protonated amino acids -use chromatography to separate
Ester hydrolysis- alkaline
-produces carboxylate salt BUT goes to completion!!! C₂H₅COOCH₃ + NaOH → C₂H₅COO⁻Na⁺ + CH₃OH then add acid C₂H₅COONa + H⁺ → C₂H₅COOH + Na⁺
Benzene - reaction mechanisms
-reacts via electrophilic substitution as it is electron rich due to delocalised e⁻ in 𝜋 bond (electrophile is Y⁺) 1) as Y⁺ approaches, 2e⁻ out of 6e⁻ in ring are attracted ∴ forms intermediate compound with +ve charge and partially full ring. 2) Intermediate not stable therefore Hydrogen leaves as H+ and electron pair returned to delocalised ring
Organic Synthesis Techniques - separating funnel & solvent extraction/washing
-separate immiscible liquids - Add mixture to separating funnel and add chosen solvent -agitate -allow contents to settle -open tap and collect layers (form based on density) -washing with solvent to dissolve impurities
Organic Synthesis Techniques - Steam Distillation
-separate insoluble liquid from aqueous solution -pass steam into reaction mixture= agitation from steam endures both liquid and solution on surface of mixture -good as allows separation below boiling point = ↓ chance of organic decomposing
Organic Synthesis Techniques - Simple& Fractional Distillation
-simple= heat mixture in flask, liquid with ↓ bp boil first and pass into condenser & collect. thermometer - if temp steady then compound distilled, if rising then new compound distilled -fractional - add fractionating column filled with glass beads to improve purity of final product
Amide Functional group and properties?
-solid @ RTP (methyl amide is liquid) -↓ Chain soluble in water as 2 electronegative elements joined to central carbon = perm dipole and H-Bond with water -Carbon very electron deficient
Amides and polymerisation
-undergo condensation polymerisation 1) Di-carboxylic acid & diamine = eliminate H₂O & form amide bond in POLYAMIDE 2) can also use diacyl chloride + diamine = eliminate HCl
Polarimetry
-uses plane polarized light to measure the optical activity of light 1) monochromatic light source shines light = through a polaroid filter = polarizes light 2) plane polarized light passes through sample of solution -if optically active, plane of polarized light rotated clockwise = dextrorotatory anti clockwise = laevorotatory
Aldehyde oxidation - 3 methods
1) Acidified potassium dichromate(VI) -orange solution to green solution (Cr₂O₇ ²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O) 2) Fehlings or Benedicts solution - blue solution → red ppt Cu²⁺ → Cu₂O 3) Tollens reagent dissolve ammonia and silver nitrate solution,add aldehyde and warm = silver mirror ppt forms Colourless solution → silver ppt 2Ag(NH₃)₂ → 2Ag + 4NH₃
Grignard reactions and products
1) CO₂ = Carboxylic acid 2) Methanal = 1° Alcohol 3) Aldehyde = 2° Alcohol 4) Ketone = 3° Alcohol -extend chain and add branches
Organic Synthesis Techniques - Filtration
1) Filter paper 2) Buchner Funnel/Reduced pressure
Preparation of primary aliphatic amines - reduction
1) Reagent: Nitrile & LiAlH₄ in dry ether CH₃CN + 4[H] → CH₃CH₂NH₂
Preparation of Carboxylic acids
1) full oxidation of 1° alcohols or aldehydes -Cr₂O₇²⁻ in acid + reflux C₂H₅OH + [O] → (+H₂O) CH₃CHO + [O] → CH₃COOH 2) Hydrolysis of nitriles (C≡N breaks, C to organic and N to ammonia/um) HEAT UNDER REFLUX with dil acid or alkali a. C₂H₅CN + H⁺ + 2H₂O → C₂H₅COOH + NH₄⁺ b.C₂H₅CN + OH⁻ + H₂O → C₂H₅COO⁻ + NH₃ (add hydrogen ion) -then separate via fractional distillation
How to extend a carbon chain
1) halogenoalkane + cyanide 2) Carbonyl and Cyanide 3) Alkylation of benzene 4) Grignard Reagents
Organic Synthesis Techniques - Recrystalisation
1) impure solid is dissolved in minimum volume of hot solvent 2) Solution filtered = remove insoluble impurities 3) Solution cooled and filtered = organic solid crystallises and soluble impurities removed -filtered using buchner funnel 4) While being filtered, solid washed with ice cold solvent = remove impurities on surface of solid crystals but solid does not dissolve as solvent cold 5) leave to dry
Organic Synthesis Techniques - Drying
1) solid = either leave inn warm place or use desiccator (container with lid and drying agent in bottom) 2) organic product - use anhydrous calcium chloride or sodium sulfate = absorb water so solution cloudy → colourless
Preparation of primary aliphatic amines - Methods
1)Nucleophilic substitution of Haloalkanes 2)Reduction of Nitriles
Carbonyl & 24DNPH
2,4 Dinitrophenylhydrazine reacts with carbonyl group to form 24DNPH derivative (carbonyl loses O and attaches to 24DNPH -H₂) = red/orange ppt -zine → zone -derivative ppt have characteristic mp and therefore can be used to figure out compound
Amino Acid - Properties and Isoelectric point
2-amino acid -can act as acid (donate H⁺ via carboxylic acid end) or base (Amine group accept H⁺) -isoelectic point - pH at which you can find zwitterions of amino acid -if ↑ pI, solution has ↑ pH as molecule primarily base, other way for low pI
Benzene Keluke structure & problems
3 C=C, 3 C-C 1) did not decorous bromine water 2)only 3 dibromobenzene isomers 3) bond lengths and electron density symmetrical 4) enthalpy of hydrogenation more thermodynamically stable than it should be
Racemic mixture
50/50 mixture of 2 enantiomers = mixture is not optical active overall
How to aldehydes and ketones react?
Aldehyde - reduced to 1° alcohol, oxidized to carboxylic acid Ketone - reduced to 2° alcohol, CANNOT BE OXIDISED
Amine & Halo-alkane
Amine substitution Conditions : Heat under reflux 1) C₂H₅NH₂ + C₂H₅Br → (C₂H₅)₂NH + HBr 2) (C₂H₅)₂NH + C₂H₅Br → (C₂H₅)₃N + HBr Furthur Sub (C₂H₅)₃N + C₂H₅Br → (C₂H₅)₄N⁺Br⁻
Amines and copper ions
Amines can acts as ligands as they have lp (like ammonia) a. [Cu(H₂O)₆]²⁺ + 2 C₄H₉NH₂ → [Cu(H₂O)₄(OH)₂] + 2 C₄H₉NH₃⁺ = light blue ppt b [Cu(H₂O)₄(OH)₂] + 4 C₄H₉NH₂ → [Cu(C₄H₉NH₂)₄(OH)₂] ²⁺ + 2H₂O + 2OH⁻
Amines and water
Amines react with water to form basic solutions -dissolve in water as can form H-bonds -can accept H⁺ by dative bond with nitrogen CH₃NH₂ + H₂O ⇌ CH₃NH₃⁺ + OH⁻
Carbonyl group - bonding
C=O - polar so molecules may have perm dipole-dipole forces BUT NO H BONDS
Acyl Chloride
Carbon is attached to 2 very electronegative atoms ∴ electron deficient and open to nucleophilic attack
Carboxylic acid reaction - esterification
Carboxylic acid + alcohol (w/acid catalyst of conc. sulphuric acid) ⇋ ester + water
Stereoisomerism
Compounds with the same molecular and structural formula but a different arrangement of atoms in space
Benzene - Properties
C₆H₆ -colourless arene liquid -bp 80C -insoluble in water -toxic
What does the difference in hydrogenation enthalpy of benzene tell us about its structure?
Difference in stability of about -152 kj mol, There is not 3 xC=C bonds but rather each carbon atom donates 1electron to the delocalised pi bond. This delocalised bond increases the stability of the ring structure = substitution rather than addition
Benzene - Acylation
Friedel Craft *reagent* - ethanoyl chloride *conditions* - heat under reflux in anhydrous 1) AlCl₃ + CH₃COCl → AlCl₄⁻ + CH₃CO ⁺ 2)CH₃CO ⁺ electrophile 3) makes HCl
Benzene - Alkylation
Friedel craft *reagent* - haloalkane + AlCl₃ Catalyst *conditions* - dry and anhydrous, RTP 1) AlCl₃ + RX → AlCl₃X ⁻ + R⁺ 2) R ⁺ attacks as electrophile 3) Forms HCl + alkyl benzene
HPLC
High Pressure Liquid Chromatography Stationary:silica packed in tube (smaller particle = ↑ separation) mobile - high pressure liquid solvent 1) Sample injected into tube 2) Solvent forced under ↑ pressure 3) DIFFERENT RETENTION TIME = detect via UV :) fast, automated, can be connected to mass spec
Ester - hydrolysis
Hydrolyse with water/split with water ⇌ Carboxylic acid and alcohol -reversible - slow
Benzene - Hydrogenation
Mix with hydrogen and heat under pressure with a nickel catalyst C₆H₆ + 3H₂ → C₆H₁₂
Benzene - current model
Orbitals hybridise to SP₂ ∴ each carbon atom gives 1 electron to delocalised 𝜋 ring above and below carbons solves problems !
Why is phenol more reactive than benzene?
Phenol has a hydroxyl group attached to the benzene ring. The oxygen in the hydroxyl grop has a line pair of electrons which it donates to the delocalised pi bond, thus increasing the electron density of the pi bond and increasing reactivity
Preparation of an amide
Reagent : Acyl Chloride + Ammonia Conditions : Reaction very vigorous @ RTP Equation : CH₃COCl + NH₃ → CH₃CONH₂ + HCl
Amine + acyl Chloride
Reagent : Ethanoyl chloride +butylamine Conditions : RTP Type of reaction : addition-elimination as 2 molecules joined, 1 small molecule eliminated CH₃COCl + C₄H₉NH₂ → CH₃CONHC₄H₉ + HCl N-butyl ethanamide = buty group attached to N, 2 carbons from acyl chloride and its an amide
Preparation of primary aliphatic amines - Nucleophilic Sub & how to prevent further substitution
Reagent : Haloalkane and AQUEOUS ALCOHOLIC Ammonia Conditions: a. heat under reflux with conc ammonia in a sealed tube under pressure CH₃Cl + NH₃ → CH₃NH₂ + HCl (or salt) -can further sub as amine has lone pair on nitrogen ∴ use excess ammonia CH₃Cl + 2NH₃ → CH₃NH₂ + NH₄Cl
Preparation of aromatic amines
Reagent : nitrobenzene & Acidified Tin(Sn + HCl) Conditions : heat under reflux C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O -or add alkali to phenyl-ammonium ion C₆H₅NH₃⁺ + OH⁻→C₆H₅NH₂ + H₂O
carbonyl reduction
Reduced using LiAlH₄ (lithium aluminum hydride) dissolved in dry ether e.g. C₂H₅CHO + 2[H] → C₃H₇OH
Rf
Retention factor = distance moved by solute/solvent -same for every time per solute if using same conditions -may need to measure using uv or dye for organic as colourless Limitations : components similar Rf & no Rf value may be recorded before
Gas Liquid Chromatography
Stationary : liquid or metal inside tube Mobile: inert gas (Ne/He) 1) inject small sample & boil to vaporise 2) force inert gas under pressure through sample 3) components have different retention times and thus detected by UV at different times -rate depends on attraction to stationary phase
Column chromatography
Stationary : silica packed into burette mobile : solvent 1) Soak stationary phase in solvent 2) add mixture to top of tube and open tap 3) components travel through column at different times depending on attraction to solvent and stationary phase 4) top up solvent 5) collect component at end and further analyse
TLC
Stationary phase : silica mounted on plastic mobile : solvent
Optical isomerism
Type of stereoisomerism - caused by chiral carbon centre in a molecule -Optical isomers are mirror non-superimposable images of one another
Benzene - Bromination
Use FeCl₃/Br₃ as catalyst heat under reflux
Chromatography - stationary & mobile phase
Used to separate and analyse small amounts of mixtures -stationary : phase that does not move -mobile : component that moves through stationary phase and transport substances
Zwitterion
a molecule containing both a positive and negative charge, leading to no overall net charge -↑ intermolecular forces ∴ ↑ MP/BP
Chiral
an atom in a molecule that allows it to exist in non-superimposable forms e.g. chiral Carbon centre with 4 different functional groups
Amino-acid and chirality
apart from glycine, all amino acids contain a a chiral carbon centre, ∴ all have optical isomerism. If its synthesised in a lab, a racemic mixture formed
Benzene - Combustion
burns with a yellow sooty flame due to ↑ C:H
SN1 & optical activity via nucleophilic substitution
carbocation is planar = equal chance nucleophile will attack from left or right = racemic mixture formed
Chromatography - how?
each component of mixture attracted to both mobile and stationary phone but different in strength 1) strong to stationary = ↓ movement 2) Strong to mobile = ↑ movement
Addition polymerisation dicarboxylic acid and diol
ester bond -OH lost from acid H lost from alcohol forms water
Name ester
first part from alcohol second part from carboxylate salt e.g. methanoic acid + ethanol → ethyl methanoate + water
Carboxylic acid reaction - Halogenation
form acyl chloride PCl₅ + Carboxylic acid → POCl₃ + HCl + acid chloride -anhydrous as PCl₅ react with water -HCl= misty fumes =test for OH
Amines + acid
form ammonium quarternary ionic salts CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻
Condensation polymerisation
formation of a polymer by the reaction of 2 monomers in which a small molecule is also lost - usually water or HCL -e.g. ester link
Phenol & bromine + explanations
forms 2,4,6 tribromophenol at RTP -oxygen in OH has a lp that can merge with delocalised 𝜋 bond = ↑ electron density above and below ring = ↑ reactive as Br₂ polarised when approaches ring → Br⁺ + Br⁻ -OH = ring activating
Ester synthesis
from Carboxylic Acid - slower, reversible and ↓ yield from Acyl chloride - faster, better yield but must be dry
Ester hydrolysis- acidic
hydrolyse with water and add sulphuric acid catalyst to speed up -doesnt affect position of equilibrium
Carbonyl - Iodoform - how, what does it show?
if CH₃CO present, reacts with Iodine alkaline solution to form CHI₃ = yellow ppt CH₃C=OR' + 3I2 + 4OH- → CHI₃ + R'COO- + 3I- + 3H2O
Organic Synthesis Techniques - Purity = bp
impurities ↑ bp -simple distillation and compare to data book value -may not be conclusive as cannot measure v-accuratly + some organic compounds have same bp
Solubility of carbonyl groups
low chain aldehyde/ketone can form H bonds with water ∴ dissolve -long chain ↓ soluble
Carboxylic acid reaction - carboxylate salt
neutralisation reaction with base 2CH₃COOH + Na₂CO₃ → 2 CH₃COO⁻Na⁺ + CO₂ + H₂O
Addition Polymerisation
no loss of atoms ∴ all atoms of monomer in polymer
Optical isomers
non superimposable images of molecules - mirror images as they are asymmetric.
Aldehyde
on terminal carbon
Enantiomers
optically active isomers -only distinguished by experimentation
Carboxylic acids - bonding and solubility/boiling point
polar C=O & O-H bonds -can form H bonds with water therefore small chain dissolve. long chain less soluble as HC chain is bigger -relatively high bp as H bonds + dimers ACTS AS WEAK ACID
Carboxylic acid reaction - reduction
reduced to aldehyde = immediately further to 1° alcohol LiAlH₄ in dry ether CH₃COOH + 4[H] → C₂H₅OH + H₂O
Paper Chromatography
stationary : paper mobile : solvent 1) plase sample on paper on base line (in pencil) 2) dip paper into solvent (depth < base line) 3) place in container with lid to prevent solvent evaporation 4) lat solvent run up paper = dry and analyse (may need to use dye e.g. ninhydrin as organic colourless)
Sn2 & optical activity
when partial bonds form - product fomred is enantiomer e.g. if reactant is dextro-, product is leave ∴ can see which mechanism
