Question

(a) Draw the saw-horse (or wedge-dash) projection of (2S,3R)-3-methylpentan-2-ol. [Marks: 1] (b) Draw the Newman projections of the 2-3 bond in (2S,3R)-3-methylpentan-2-ol. [Marks: 2] (c) Based on the Newman projections from part b. - draw a rotation vs. energy diagram (you do NOT need to give specific energy values in this diagram) that will allow you to identify the most stable confirmation around the 2-3 bond. Assume the greatest steric and torsional strain occurs when the hydroxyl and ethyl groups align. [Marks: 1] (d) What kind of reaction would occur if you added a strong acid to (2S,3R)-3- methylpentan-2-ol? Explain the mechanism of this reaction assuming that the reaction has first order rate kinetics.

Answer 1

lo dras wedge dash easy Rule 1. vertical roups are auday from observer & drawn as dash Rule 2 Hori zontal roups are tosards observer & draon as wedge C2 н OH И: OH (25) En(CHs) ns CH(CH) CHS CH (OH)CH3 CH(on)Cn CH CнЗ и Н (3R) (X) CHs oM CH3 d) Combining the tao e get OH н Noti'ce in crrce part contiguraln is inversed an compar H' tb ib lndividualfgure gien above(X)

3 (b) Newman prejection fos3 2-Mdhygetan2- Hod the model, sa that C2,C3 ae in one ine with Съ eye, c2 (favther) is drawn as cirde & H C3 (nearer)as dot () OH CHy HG CHy CHs OM OH OM 360 3o0 240 18o 120 600 CzHS А нои HO 3H (a) Addition f strong acid ke conc Hso, would underge dehydration (elimination) to give alrene (sytzeff ule) CH3 и OH .cHs 3-Methylpent-2-ene Conc. CHS H (M)

4A Mechanism stef 1: Protonation of-H roup CH:H M Step. 2: Removal of Ho, formation f carbo cation -C HCH,t0 CH3 Step3: Deprotonation of carbocation to alkene H

a) first we will dras the Fischer's Prjection R S At C-2 C-2 H- C2 H- OH C3 H- 2CH (CH (1) CM3 čn,CH 1 n(on)CHS SR At C-3 C-3 H (2) Gelden rule: decide the sequence Priorities without making any interahange,if the lousest priort atbm /group is on verical line, then thi will actual configuration, if on horizontal line (as in present case ()) then change the confiration obtained from R to S orice versa to et actual Combig ation as in (1) Sequence is OH CHCH CH RS chanye R to S, as lowest eri P anhaizon (2) Similarly tr (2), it is S& as the louest frinily gtoup n on haizntal line,s change to R