TOPIC 17/18 - MORE ORGANIC

A molecule with a chiral carbon atom and has 4 different groups attached. And a chiral molecule is one that has no plane of symmetry so can get 2 non-superimposable mirror images - different properties btw enantiomers.

A carbon atom bonded with 4 different groups attached to it (asymmetric). A chiral center can be identified by asterisks by it. EASY TO IDENTIFY IF DRAW IN DISPLAYED FORMULA.

• come under stereoisomerism - same molecular formula but atoms are arranged spatially different. • OCCURS when molecules have a chiral centre - get 2 non-superimposable mirror images (asymmetrical) leads to 2 possible isomers. • draw mirror plane

• when not bonded to 4 different atoms or different groups of atoms. • as 2 groups are same. • there is C=C bond • 2 chiral centres = form 4 optical isomers = 4 non- super imposable images

OPTICALLY ACTIVE (single enntionmers) racemic is mixture of 2 enantiomers

The ability of a single optical isomer to rotate the plane of plane- polarised monochromatic light in molecules containing a single chiral centre. (so angle of plane of oscillation rotates - EM rad - transverse waves - right angles)

• monochromatic light source can pass through polarising filter it absorbs oscillations except in a single plane - POLARISER which CONVERTS unpolarised to plane-polarised light. • plane-polarised light passes through sample tube if subst optically active - plane-polarised light roates. • second polarisng light - analyser measure angle of rotation.

Dextrorotatory (C next to D)

LAEVOrotatory

The 50:50 mixture or equal concentrations of two enantiomers that have no optical activity. • planar structure also due to attack on either side • the rotation in plane of polarised light in opposite directions cause (distinguish btw stereoisomers) and Cancel out each others light rotating effect IF NOT IN EQUAL AMOUNTS - chiral molecules only show optical activity if 1 isomer present in a greater quantity.

like 1 enantiomer can have 1 benefical effect and the other can be harmful.

• S=Substitution, N=nucleophilic , 1=unimolecular (1 species involved in Rate Determining step (1) step SLOWEST. • Mainly in 2’ and 3’ C-X • equal chance of being attacked by nucleophile by EITHER SIDE to: • Forms two products • It can form a racemic mixture as equal concentrations of opposite enantiomers are formed - NO optical act. • tetrahedral shape -> planar • carbocation intermediate formation after Cs+-Xs- polarizes.

• STERIC HINDERANCE as more S.H , more Nucleophilic attack - increase Rate determining step. GRAPH: - The Ea required to form carbocation intermediate much greater than step 2 attack of nucleophile to carbocation - much faster

-S=Substituiton, N=Nucleophillic, 2=bimolecular: - tempoarary formation Nu & C bond - C-X bond breaking ALL IN TRANSITION STATE - Mainly in 1’ and 2’ haloalkanes. - Nu attack on 1 side. - PRODUCT is an INVERSION of Reactant SO has OPPOSITE optical activity. - Dextrot enant as REACTANTS as Laevorot enant Prod -If the molecule is an enantiomer it will reverse the way in which it rotates the polarised light

• primary carbocation formed and more energetically unstable - INSTABLE requires higher level of Ea so by undergoing SN2 reaction the Ea is lowered.

• Aldehyde has C=0 at end of C chain • Ketone has C=O in btw R chain C=O has lower priority so give lower no. than methyl group

No because they do not have a hydrogen attached to O,N or fluorine a highly electronegative group only LF, chain increases, Mr and e- increases, higher density so greater polarity. - ethanoic acid > ethanol

yes, functional group allows it as energy able to compensate for it and capable to disrupt H bond in water. As chain length increases, solubiltiy decreases , alkyl chain incr, less energy needed

2,4-DNP (DiNitroPhenylhydrazine) transparent Positive result: Bright Orange Percipitate hydrazone

Fehling’s or Benedict’s solution, Tollens’ reagent and acidified K dichromate(VI) ions = ALL OXIDISING AGENT. • warmed BRICK RED = ALDEHYDE, BLUE = KETONE • ammonical silver nitrate (NaOH + AgNO3 add dil NH3) - silver mirror formed for ALDEHYDE when gently warmed. REDOX react Ag+ reduced • orange to GREEN - reduced Cr

• Filter, dry and purify the derivative 2,4-DNP • Measure the melting point of the derivative • Compare the value to a data booklet and check which carbonyl compound it belongs too

• aldehyde and ketone and some alcohols • Has to have C=O next to a CH3 to give +ve result which is a pale yellow precip (insoluble solid) , due to reaction of I2 in alkaline sol.

REDUCING AGENT so [H] - explosive in H20 - reduces carboxylic acids and aldehyde and ketone back into 1’ and 2’ alcohol. so 2[H] - Rapidly reacts impossible to stop halfway so would not be able to get aldehyde from carboxylic acid • nitrile into primary amine

• C=O dipole susceptible to nucleophilic attack • pi bond in C=O breaks and reactive intermmediate prod forms • extra pair of e- on O donated to neighbouring H atom. • source of hydride ions and forms ALOCHOL due to Reducing agent.