I am installing a new toilet in a remodeled bathroom. The toilet is going to be placed where I cannot instal a vent pipe greater than 1.5" diameter because of existing obstructions. I understand that a vent pipe for a toilet should be 2" diameter minimum. Will the toilet flush properly with this small vent pipe?
Thanks for the benefit of your experience.

I don't have your answer but I have moved you back to the head of the list. If Speedball1 doesn't catch this Friday morning you might send him a IM, he's listed as the #1 plumbing expert, actually #1 expert out of all of us not matter the topic. My personal read is that your toilet should have a 3" or 4" vent, 1.5" will give you some gurgling and chugging but Tom will know better.

A lot of this depends on the developed length of the 1-1/2 run -- If we're talking nine or ten feet before tying into a larger vent, then the 1-1/2 will likely do fine if it's all vertical.

Have you considered using 2" copper DWV pipe?

2" copper DWV pipe is about an eighth inch thicker than 1-1/2 IPS piping.

You would need a proper transition band (a shielded coupling) to transition from the 2" IPS to 2" DWV, but at least the internal diameter would still be a full 2".

I agree with growler that a 2" vent's better then a 1 1/2 one. Having said that my cose book, ( Standard Plumbing Code, Chapter 14, Section 1421.2 tells me that a 1 1/2" vent will service 10 fixture units at a maximun vent length of 100 feet. A water closet equals 4 fixture units. I ran into the same problem as Alan Bee some 30 years ago while roughing in a large church with 6 bathrooms. Because of space restrictions I vented 2 urinals,(8 fixture units) with a 1 1/2" vent. The inspector passed it but warned me that in the future he would prefer the vents to be at least 2".
On another note, Thanks Bob for those kind words but I don't consider myself the top anything on this page. All the heavy posters,( and you know who you are) on this page are #1 top experts, You guys are out in the field working with new equipment and learning new procedures while I'm retired and out of the loop. While my plumbing experience might go back farther and I can draw on that youall are out there doing new things and using new equipment. You have knowledge that I do not and I think that should be recognized and applauded. I shall now climb down from my soap box. Regards to all, Tom