Radicals Answers PDF

Problems Identify the product of this reaction and draw the mechanism Draw the radical formed from addition of R˙ to vinyl acetate (VA) and methyl acrylate (MA). Use frontier orbitals to rationalise why VA radicals prefer to react with MA whilst MA radicals prefer to react with VA Draw a mechanism f...

Problems Identify the product of this reaction and draw the mechanism Draw the radical formed from addition of R˙ to vinyl acetate (VA) and methyl acrylate (MA). Use frontier orbitals to rationalise why VA radicals prefer to react with MA whilst MA radicals prefer to react with VA Draw a mechanism for the following transformations 1 Problems Identify the product of this reaction and draw the mechanism Radical chain mechanism leading to the 5-exo (kinetic) cyclisation product. Step 1 – decomposition of the initiator AIBN Step 2 – radical abstraction of H from Bu3SnH to form the tin radical chain carrier (initiation) Step 3 – radical abstraction of the Br using the tin radical leading to a primary alkyl radical (initiation) Step 4 – 5-exo cyclisation (propagation) Step 5 – H abstraction from Bu3SnH by the resulting alkyl radical regenerating the tin radical chain carrier. Draw the radical formed from addition of R˙ to vinyl acetate (VA) and methyl acrylate (MA). Use frontier orbitals to rationalise why VA radicals prefer to react with MA whilst MA radicals prefer to react with VA Radicals formed = VA radical is relatively electron-rich giving a higher energy SOMO and better interaction with the LUMO of the electron-poor alkene of the MA. Conversely, the MA radical is relatively electron-poor (due withdrawing effect of the adjacent carbonyl), giving a lower energy SOMO which preferentially interacts with the HOMO of the electron-rich alkene of VA. Draw a mechanism for the following transformation Radical chain mechanism again. In this case the radical cascades to the polycyclic product via sequential 5-exo-trig and 5-exo-dig cyclisations. Step 1 – decomposition of the initiator AIBN Step 2 – radical abstraction of H from Bu3SnH to form the tin radical chain carrier (initiation) Step 3 - radical abstraction of the Br using the tin radical leading to a tertiary alkyl radical (initiation) Step 4 – 5-exo-trig cyclisation (propagation) Step 5 – 5-exo-dig cyclisation (propagation) Step 6 - H abstraction from Bu3SnH by the resulting alkyl radical regenerating the tin radical chain carrier. Draw a mechanism for the following transformation Radical chain mechanism again. In this case we have to consider the likelihood of a 1,5-radical translocation prior to sequential 5exo-dig and 5-exo-trig cyclisations. Step 1 – decomposition of the initiator AIBN Step 2 – radical abstraction of H from Bu3SnH to form the tin radical chain carrier (initiation) Step 3 - radical abstraction of the Br using the tin radical leading to an aryl radical (initiation) Step 4 – number the chain and identify weather cyclisation or translocation of the radical is probable. Remember the magic number 5 and radical stability drives translocation. Here the vinyl radical becomes a tertiary alkyl radical, so much more stable Step 5 - number the chain and identify weather cyclisation or translocation of the radical is probable. Remember that translocation is driven by formation of a more stable radical, whilst cyclisation is a kinetic process. Here 5-exo-dig cyclisation occurs. Step 6 - number the chain and identify weather cyclisation or translocation of the radical is probable. Here 5-exo-trig cyclisation occurs. Recall that the rate of 5-exo > 6-endo cyclisation. Step 6 - H abstraction from Bu3SnH by the resulting alkyl radical regenerating the tin radical chain carrier.