1-2: ORGANIC CHEMISTRY (Def's & FG's) Flashcards
Heteroatom
atom other than C or H in organic molecules
functional group
- part of molecule containing heteroatom
- responsible for chemical reactivity
nucleophile
electronegative functional group with LP of e to form covalent bond
electrophile
- e deficient functional group which can accept a pair of e to form a covalent bond
- must have an empty orbital
polarised bonds
e not shared evenly between two joint atoms ie. bond has a dipole
polarisability
measure of ease of distortion of e distribution
electronegativity
measure of how strong the atom attracts e
H bonding
non-covalent bond resulting in electrostatic attraction between proton attached to heteroatom and electronegative atom in another functional group
leaving group
part of molecule which takes bonding e when the bond is broken
resonance
- when more than one arrangement of double bonds needs to be drawn in order to show the electronic distribution
- molecule exists as a resonance hybrid (e.g. aromatic compounds)
aromaticity
compound must be planar and cyclic and have (4n+2) delocalised pi e
tautomers
structural isomers that differ only in the position of a H and a double bonds (e.g. keto to enol; imine to enamine)
tautomerisation
- conversion of one tautomer to its structural isomer
- its a reversible reaction
hybridisation
- the mixing of atomic orbitals to make molecular orbitals
- the shape/orientation of hybrid orbitals is optimized for bond formation
determining hybridisation
- AX2 = sp
- AX3 = sp2
- AX4 = sp3
of atoms bonded + # of lone pairs = 2,3,4 (sp, sp2, sp3)
sp3
- 4 identical hybrid orbitals (1x2s + 3x2p)
- tetrahedron
- single bond by head-on overlap
- if fewer than 4 bonds required to satisfy valence requirements, one or more of sp3 hybrid orbitals will not be involved in bonding but instead contains LP of e
- LP is potentially basic and/or nucleophilic; frequently involved in H-bonding
sp2
- 3 identical hybrid orbitals (p-orbital not invovled in hybridisation is at right angle to plane of hybrid) (1x2s + 2x2p + 1x2p separate)
- trigonal planar
- single bond by head on overlap
- double bond by sideways overlap of p orbital
- always found in double bonds (also found in partial double bonds)
Single bond O functional group
- e.g. alcohol
- tetrahedron
- sp3
- 2 LP on O usually involved in H-bonding
- not a good base so does not protonate
- nucleophile only when LP is not involved in H-bonding
double bond O functional group
- e.g. carboxylic acid
- O in carbonyl is not reactive because proton is readily removed
- carbonyl is sp2 trigonal planar
- O is more electronegative so s- and C is s+
- electrophilic carbonyl C; nucleophile can attack from top or bottom of plane
- carboxylates are -ve charged at physiological pH so can behave as bases
- Ca,Cc,=O,H are in the same plane
- Ca is nucleophilic provided it has H that can be removed
aldehydes vs ketones
- aldehyde is R-C=H
- ketone is R-C=R
- in aldehyde, nucleophilic attack is v. easy as no hindrance
- more reactive than ketone due to steric reasons
- ketone less reactive due to electronic reasons as C is able via inductive effect (2 alkyl groups) to share e cloud with Cc which partly quenches s+ charge compared to having an H
keto to enolate tautomerisation
- Ca hybridisation changes from sp3 to sp2 as base removes H
- usually carbanion is v.unstable but in this case -ve charge can delocalise over carbonyl system to form enolate anion
ester
- carboxylic acid + alcohol
- R-C=OR (-OR; -NR; -SR)
- Ca in O ester is less acidic thus less reactive than in aldehyde/ketone
- harder to remove the proton because the enolate anion is less stable because the O of the ester will be sharing its e in the carbonyl system so will be competing
- sp2 not sp3 as it has most stable electronic configuration; trigonal planar shape
amine
- 1LP on N
- R-NH2
- sp3 tetrahedron
- nucleophile only if proton is removed
- acts as base when deprotonated
- pka 8,9,10 so at physiological pH is protonated –this is why amino acid side chains act as acids in chemical reactions
amide
- R-C=ONH2
- peptide bond is planar because N is sp2
- sp2 hybridisation of N promotes delocalisation of LP and reduces electrophilicity of Cc so less reactive than aldehydes/ketones
