Hi Regina!

The molecule actually DOES have alpha hydrogens on both sides of the carbonyl group.  The carbonyl carbon is bonded to two carbons, called alpha carbons.  Each alpha carbon is bonded to two hydrgens, called alpha hydrogens.  So we have four alpha hydrogens in the molecule.

To depict the mechanism, only one of the alpha hydrogens are shown so as not to clutter the drawing.  The other three alpha hydrogens are understood to be there in a skeletal structure.  In other words, each carbon implicitly has enough hydrogens to give it a total of four bonds.

-Ben

Hi Isabella!

In order to get E2 elimination, one must use a base that is strong enough to deprotonate a carbon that neighbors the carbon bearing the bromine atom.  Cyanide ion is a very good nucleophile, but it's not a very strong base, which favors SN2 substitution over E2 elimination.

-Ben

Hi Amanda!

A bridgehead carbon is one that is shared by both rings of the bicyclic molecule.

The Cahn Ingold Prelog sequence rules rank priority according to atomic number. If we take the top bridghead carbon, for instance, we see that it is bonded to a hydrogen and three carbons.  The hydrogen, since it's lower in atomic number than the three carbons, is the lowest priority.  The other three carbons are equivalent, so the next step is to look at the second, third, fourth atoms away from the chiral center until the first difference is found.

Being closer to the bridgehead means higher priority, in this case, because the closer you are to the bridgehead, the sooner you find the higher atomic number atoms that give the substituent a higher priority.

Hope this helps!

-Ben

Hi Tito!

No, it doesn't matter which way you look at the molecule.  The question indicates which bond should have the front and back carbons of the Newman projection, but it doesn't specify the direction.

-Ben

Hydroxide ions do not protonate hydronium ions.  If this was the case, you'd end up with H_4O+ and O-, both of which are very unstable.Instead, you have hydronium ions protonating hydroxide ions.  If one hydronium ion protonates one hydroxide ion, two water molecules are produced.  The reverse reaction also occurs--two water molecules reacting with one another to form one hydronium ion and one hydroxide ion.Whichever acid is stronger (hydronium ion or the "acid itself") will protonate the base.  Since hydronium ion has a pKa of 0, and since lower pKa means stronger acid, any acid with a negative pKa will out-compete hydronium ion and react with the base.Does that answer your question?-Ben