Question

need help with 14-21

Stereochemistry of the Su2 reaction In the Sn2 reaction the tetrahedral carbon center is inverted. We describe the mechanism as nudeophilic (Nuc) back side attack; the leaving group (LG) is leav ing from the front side. Generally, the LG and the Nucare electron rich so it would be unfavorable for them to react from the same side (charge repuls ion). The geometry of the carbon at the transition state is trigonal planar. 14) Label the 2-bromobuta ne below with the R or S designation 15) Provide the product for the following step. Br: CEN 16) Are the priorities of a Brand a CN both 1 in their respective molecules? 17) Label the chiral carbon in the nitrile above with the R or S design ation. Stereochemistry of the E1 reaction Recall that the E1 reaction goes through an alkyl carbocation intermediate and abstraction of a neighboring proton (there may be more than one) results in an alkene. There is also free rotation around the bond axis, which means that E/Z isomers are possible 18) Provide the three potential alkenes for the step below. Н,с 19) Of the above alkenes, which is most stable? Which alkene would you predict to be the major product? Stereospecificity of the E2 reaction The E2 elimination of H and LG to form an alkene occurs in one step. In order for this to work the LG and the H need to be aligned properly (anti-coplanar). Think back to Newman projections these will be helpful to determine the stereochemistry of E2 eliminations 20) Draw the three st agge red Newman projections for the following molecule looking down the C2-C3 bond. Br 21) Which of the three have the H aligned anti to the LG (bromide)?

Answer 1

Dis keor borm dash om CN +B70 CEN -CN H Both Br & CN Priony due malecules t0 an gvem wegas 1 her gurt atimic Arany abstracteal B7 CH3 4 CH3 CHy I & 3