s&r topic 3 Flashcards
what is an inductive effect
an electron-withdrawing or electron-donating electron effect caused by the polarisation of a sigma bond
affects electron density in a bond
what inductive effect do electronegative substituents give
give examples
withdrawing effect
halogens, nitriles, nitro-compounds, ammonium, carbonyls
what inductive effect do electropositive substituents give
give exmaples
donating effect
alkyl groups, CO2, organometallic compounds
give the order of electronegativity of the hybridised carbons
why is this the order
C sp > C sp2 > C sp3
sp is the most electronegative because
- s-orbital is lowest energy orbital
- sp hybrid has most s-character and so lowest in energy
- over energy hybrid is the most electronegative
why is electronegativity used in heterolytic bond breaking
the electronegativity of atoms involved in the bond determine the stability and reactivity of ions after breaking of the bond
in heterolytic bond cleavage, where does the pair of electron go to
how does electronegativity affect the stability of the anion formed from the bond breaking?
the pair of electrons from the bond go to the more electronegative atom
the more electronegative this atom is, the more stable the anion will be
which carbocation is most stable and why
the tertiary carbocation is more stable
- it is bonded to three alkyl groups
- alkyl groups have greater electron-donating inductive effect than H
- carbocation receives some-electron donating effects, which stabilises it
define hyperconjugation
how does the tertiary carbocation experience hyperconjugation
hyperconjugation - delocalisation of electron across sigma and pi systems or p-orbitals, leads to a stabilised molecule
in tertiary carbocation, the C+ has an empty p-orbital that is parallel to the σ(C-H) on the next carbon, the electrons are delocalised across these two areas and carbocation is stabilised
what does there resonance arrow look like
↔︎
what are different forms/structures of molecules called when undergoing resonance
canonical forms or resonance forms
when a sample undergoes resonance, what is the true structure of the overall sample
it is a resonance hybrid, which is a structure directly between the two resonance forms, an average illustration of all resonance forms
not meaning the molecule is flicking from each resonance form
which bonds stay the same when drawing resonance forms and which ones change
resonance forms have the same σ-bonds
but different π-bonds
resonance only involves pi-systems and negative and positive charges
what is mesomeric effect
distribution of electrons in π-bonds
what is an +M effect
electron donating
stabilises cation
electrons are distributed from lone pair or π-system to cation
see topic3 vid2 for examples
what is an -M effect
electron withdrawing
stabilises anions
anions distribute their electron density into a π-system
