carbon carbon bonds Flashcards
why are organometallics nucleophilic eg in methyl lithium
bond is polarised towards the carbon as its more electronegative, carbon develops partial negative charge (lithium has delta positive as its less electronegative)
bond polarity is determined by electronegativity of bonded atoms, electronegative atoms attract electron density in a covalent bond towards them, greater difference in electronegativity=greater degree if bond polarisation
what are organometallics used for
formation of new c-c bonds
what is formed when a ketone reacts with an organometallic
tertiary alcohol
what is formed when an aldehyde reacts with an organometallic
secondary alcohol
what is bond polarity
distribution of electrical charge between two bonded atoms
why is carbon the site for nucleophilic attack in c=o
its partially positive because the oxygen is more electronegative so it pulls the electrons towards itself so the carbon is more positive
describe the correlation between a molecules electronegativity and orbital energy
more electronegative the lower the energy of its orbitals
what charges are each atom in C-Li
C= delta negative
Li= delta positive
how are gringard reagents made
reacting magnesium turnings with alkyl halides in ether solvents, forms a solution of alkyl magnesium halide
R-X —> R-Mg-X
R=alkyl/allyl/aryl
X= I,Br,Cl
what is oxidative insertion
increases oxidation state of metal, adding magnesium between alkyl and bromine bond to make a butyl magnesium bromide, Mg
(0) to Mg (ii), Mg 2 more stable so helps drive reaction
what is THF
tetrahydrofuran
describe the characteristics of ether molecules like THF and diethylether
aprotic, polar, dont contain any acidic hydrogen atoms in their structure
what is Et2O
diethyl ether
how are organolithium reagents synthesised
oxidative insertion of lithium metal and alkyl halide, each reaction requires 2 lithium atoms to make desired organolithium and a lithium halide salt
lithium oxidation state goes from lithium 0 to lithium 1
what forms after the oxidative insertion of lithium into an alkyl halide
alkyllithium and a lithium halide
R-X——>R-Li + LiX
R=alkyl or aryl
X=Br, Cl
usesLi and THF
difference between oxidative insertion of magnesium and lithium (difference between gringard and organolithium)
lithium requires 2 Li atoms to form alkyl lithium and lithium halide salt
what does a basic solution mean
more OH- ions than H+ in solution
why do organometallics need to be kept free from moisture
organometallics are extremely strong bases and they will react rapidly to produce corresponding alkane, water acts as acid and provides proton,
what is the pKa of a C-H bond in an alkyne (triple bond cc)
~25, most acidic of the hydrocarbons
name an alternative for deprotonation
halogen metal exchange
why does halogen metal exchange work/how to determine which molecule gets the metal ion
most acidic/lower pKa (=more stable) compound will be the one with the metal compound (Li)
eg. phenyl bromide reacting with butyl lithium, butane has higher pKa than benzene so benzene is more acidic so it takes the lithium
ways to make organometallics
oxidative insertion of Mg or Li into alkyl halides, deprotonation of alkynes, organ lithiation of functionalised benzene rings, halogen metal exchange, transmetallation
how are carboxylic acids made
react organometallic reagent with carbon dioxide, must be under vigorously dry conditions
carbon dioxide is carbonyl containing compound and is acting as an electrophile
what happens when carbon dioxide reacts with water
slowly forms carbonic acid
