if he is only doing the one nap, could you try and put him down a little later, you might need to entertain a fair bit, when dd went from 2 to 1 nap we had a difficult time for about a month, she still wanted to nap at 11.30, it made the lunch thing difficult too, i gave fruit or yogurt before nap and balance after, now for the last month she is not going down until 12.30-1.00 so we do lunch midday and things are great, i am no expert, i read alto of other post, good luck to you, D's might even go back to 2 sleeps, I've heard a lot of babies drop the second sleep at about 13 to 14 months,