(Solved): Propane, the three-carbon alkane C3H8, is shown below. Make a molecular model of propane and ...

Propane, the three-carbon alkane ${\mathrm{C}}_3{\mathrm{H}}_8$, is shown below. Make a molecular model of propane and use it to work through the problems in this Assignment. (a) Draw a Newman projection of propane as viewed down a carbon-carbon bond from either end of the molecule. Convince yourself with your model set that for propane it doesn't matter whether you look down ${\mathrm{C}}_{\mathrm{I}}?{\mathrm{C}}_2$ or down ${\mathrm{C}}_3?{\mathrm{C}}_2$, you see equivalent things. (b) Starting with either an eclipsed or a staggered conformation, rotate around the $\mathrm{C}?\mathrm{C}$ bond in increments of $60^{?}$ and draw the corresponding Newman projections. (c) Are the staggered conformations all equivalent? How about the eclipsed ones? (d) Draw an energy versus dihedral angle graph like we did in class. Start by putting maxima where the eclipsed forms are and minima where the staggered forms are. (e) From our conformational analysis of ethane in class today, we know that one eclipsing $\mathrm{C}?\mathrm{H}/\mathrm{C}?\mathrm{H}$ interaction costs about $4.2\mathrm{kJ}/\mathrm{mol}$. If I now give you the additional fact that an eclipsing $\mathrm{C}?\mathrm{H}/\mathrm{C}?\mathrm{Me}$ interaction costs about $5.9\mathrm{kJ}/\mathrm{mol}$, what is the barrier to conversion of one staggered form to the next staggered form in propane. Label that barrier on your graph.