First 3 lectures Flashcards
What is diamagnetic anisotropy?
Different electronic properties in different directions
Diamagnetic anisotropy on benzene rings
π cloud - partial negative above and below
σ bonds - overlap of sp2 hybridised orbitals - partial positive charge along the equator
Ionic bonds and water
Strength of ionic bonds is significantly reduced in the presence of water due to a shell of water reducing the attraction
Why is it easier to break π bonds than σ bonds?
Electrons in π bond are further from the nuclei
What is the interaction between aromatic rings known as?
π-stacking interactions
Hybridisation of carbon with 2 single bonds and 1 double bond
sp2
Conformation
Spatial arrangement of atoms that can be interchanged by single bonds
Configuration
Arrangement of atoms in space that distinguishes between stereoisomers
How can configurations be interconverted?
By breaking covalent bonds
Why does torsional strain occur?
Presence of eclipsed bonds
Why does Van der Waals strain occur?
Due to steric strain from atoms being too close together
Why does angle strain occur?
Due to distortion of bond angles from typical values in ring systems
What is the equation for C-C bond angle?
180x(n-2)/n
How can stability of cyclic saturated hydrocarbons be judged?
Using enthalpy of combustion per CH2 unit - lowest is most stable
Easson and Steadman’s 3 points of interaction
Each group has a specific binding site and so rotation or interconversion will mean these do not match up
Why do racemic mixtures have toxic properties?
Due to the dissociative effect
What are π stacking interactions responsible for?
Specific folding patterns of proteins and results in the lipophilic side chain in the inside of the fold compared to the hydrophilic outside
What is the equation for the substituent hydrophobicity constant?
πx = LogPx - LogPh
Where Px = molecule with substituent x
Ph = molecule without substituent x
What does it mean if substituent hydrophobicity constant is negative?
The substituent is less hydrophobic than H and so increases hydrophilicity of the molecule
What does it mean if substituent hydrophobicity constant is positive?
The substituent increases the lipophilicity of the drug
What groups have a positive inductive effect?
Alkyl chains
Why do EWGs give negative inductive effect?
They decrease electron density on the ring
Why does the mesomeric effect occur?
Due to polarisation of the electrons that constitute π bonds
What groups give a postitive mesomeric effect?
Electron donating groups due to the lone pair of electrons, which can be donated and stabilise the molecule
What does the Hammett substituent constant quantify?
EDG and EWG properties
Why does Hammett substituent constant not assess ortho- effects?
Due to steric hinderance
What is the equation for Hammett substituent constant?
σ = log (Kx/KH)
What does +σ represent?
EWG
What does -σ represent?
EDG
What is the predominant effect in para?
Resonance
What does σ value depend on?
Para and meta positioning
Name of amine with 2 R groups and 1 H?
Secondary Amine
Which amine is most reactive?
Secondary amines
Why do amines have a bond angle of 107°?
Due to lone pair
Keq equation for sp3 hybridised N?
Keq = Ka reactant acid/Ka product acid
What is indicated if Keq»0?
Reaction favours products
What effect does more hydrocarbons on sp3 hybridized N have?
Lowers aqueous solubility
Why are tertiary amines less reactive than secondary amines?
Due to steric hinderance
What effect do EDGs have on the basicity of aniline?
Increase the basicity by increasing electron density on the ring
Why is aniline less basic than piperidine?
Aniline has N’s lone pair delocalised around the ring and therefore less able to bond
N’s lone pair on pyrrole?
In the π cloud so unable to bond
N’s lone pair on Pyridine?
Lone pair available for bonding
What is guanidine?
N rich functional group which is part of L-arginine amino acid
Why is Guanidine a strong base?
Due to resonance delocalisation of the positive charge present on its conjugate acid
What are quaternary salts chosen based on?
Solubility
pH of resulting solution
Strenght of ionic coupling
Ease of formation
Why is O less likely to be pronated than N?
O is more electronegative than N and therefore is less likely to share its electrons than N
Is protonation of sp3 or sp2 O easier?
sp3 as protonated ketone has a lower pKa
How do electrons occupy molecular orbitals?
In order of increasing energetic content
How can atomic orbitals be more easily combined?
If they have similar shape and energy
What is the equations for Bond Order?
Bond order = no. of bonding MOs - no. of anti-bonding MOs / 2
What are LUMO and HOMO?
Lowest occupied molecular orbital and Highest unoccupied molecular orbital
Why does O not always follow Hund’s rule?
Due to its energetic content
What orbitals are the electrons in in ground state singlet oxygen?
2 electrons in the same MO - 1 with up spin and 1 with down spin
What orbitals are the electrons in in excited state singlet oxygen?
Electrons are in seperate MOs but 1 with up spin and 1 with down spin
Multiplicity of energy levels equation
M = 2S + 1
Why is 02 2- not a radical?
All HOMO electrons are paired
What explains the paramagnetic behaviour of molecular oxygen?
MO theory predicts that oxygen is diradical
What is an alcohol with 2 OH groups known as?
Diols
Why are phenols stronger acids than alcohols?
Due to delocalisation of negative charge on the conjugate base
What do phenoxy radicals tend to do?
Tend to dimerise and end the radical chain reaction
How do ethers form explosive peroxides?
In the presence of molecular O and UV light
Why are epoxides highly reactive?
Due to torsional strain
Why are carboxylic acids acidic?
Due to resonance delocalisation of the negative charge of the carboxylate anion
Why are thiols more acidic than alcohols?
Due to its larger size and therfore better at delocalising charge
