org chem? Flashcards
Why phenol CANNOT undergo NS?
- p orbital of O atom overlaps side on with the pi e cloud of the adjacent benzene ring.
- this allows lp of e on O atom is delocalised into the ring
- leading to partial double bond character in C-O bond
- the strengthened C-O bond requires more energy to break
electronegativity in alkanes
C-H non-polar
=> lack of e rich and e deficient sites
=> unreactive towards polar reagents (thats why only got FRS)
electronegativity in alkenes
C=C bond is e rich + non-polar
=> reactive towards E+
=> thats why can undergo EA
electronegativity in RX
C-X bond is polar
=> C has partial positive charge
=> X has partial negative charge
=> partial positive C atom is E+ and susceptible to attack by Nu
electronegativity in C=O
C=O bond is polar
=> C has partial positive charge
=> O has partial negative charge
=> partial positive C atom is E+ and susceptible to attack by Nu
inductive effect in alkane
e-donating alkyl grps
=> stabilise carbon radical intermediate by
=> increasing e density of C atom w unpaired e
inductive effect on alkenes
e-donating alkyl grps
=> stabilise carbocation intermediate by
=> dispersing + charge on C atom
inductive effect on arenes
e-donating / e-withdrawing grp
=> increases/decreases e density on benzene ring
=> making ring in ___ stronger/weaker Nu than benzene
inductive effect on RX (SN1)
e-donating alkyl grps
=> stabilise carbocation intermediate by
=> dispersing + charge on C atom
inductive effect on ROH (talk abt R) vs H2O (acid)
e-donating alkyl grp
=> intensify - charge on O atom
=> RO- less stable than HO-
inductive effect on carbonyl compounds (aldehyde more E+ than ketone)
1 less e-donating alkyl grp which makes
=> carbonyl carbon in aldehyde more E+
inductive effect on CH2ClCOOH has smaller pKa than CH3COOH
e-withdrawing Cl atom
=> stabilises carboxylate anion by
=> dispersing - charge on O atom
=> CH2ClCOO- more stable than CH3COO-
Ch3NH2 is stronger base than NH3
e-donating methyl grp
=> increases e density of N atom
=> making lp of e on N atom
=> more available for donation (dative bonding w proton)
(ithink fyi)
define delocalisation
spreading of pi e over the whole system of atoms
(i think fyi)
define inductive effect
effect of e donation or withdrawal felt by polarisation of the sigma bonds of the molecule
define electronegativity
ability of an atom to attract the shared pair of e towards itself in a covalent bond
delocalisation in benzene
all C atoms sp2 hybridised
=>unhybridised p oritals of C atoms are perpendicular to ring and
=> overlap side-on to
=> form a delocalised pi e cloud
delocalisation in benzyl cation
+ charged C is sp2 hybridised
=> and has empty p orbital, which
=> overlaps side-on w pi e cloud of adjacent benzene ring
=> this allows pi e of benzene ring to be delocalised over + charged C
=> dispersing + charge
(i think fyi)
define resonance effect
the effect of withdrawing or releasing e by a substituent in a molecule as a result of contact between a lp of e and pi bond, or interaction of 2 pi bonds separated by one single bond (<- conjugated pi bonds)
define steric effeect
repulsion of e clouds of atoms dye to proximity(closeness) of arrangement in space
what to do when there is a combi of effects?
- cry
- deep breaths
- from data booklet, compare bond energy or compare activating and deactiviating grps to find out which effect is more dominant
why mp of substitiuent (a carbonyl grp) in 2nd positin smaller than that at the 4th position in phenol?
- Both got simple molecualr structure
2nd position: can form intramolecular H bonding due to close proximity of -OH in benzene ring and O atom of carbonyl grp. so less energy need to overcome less extensive intermolecular H bonding between molecules of A - draw the intramolecular bonding, must include ||||:O(partial negative), H(partial positive)
