It may be doable; whether it would be enjoyable is another question entirely. As kleeblatt notes, you haven't allowed yourself any downtime. You also don't seem to have given yourself any room for bad weather. And if you say who "we" is, I missed it -- if you are traveling with children, I'm not sure whether this plan makes sense.

If your goals in the Bernese Oberland are the Jungfrau and Schilthorn, I think it would make more sense to base in Lauterbrunnen than Interlaken. But you already have your hotel reservations?

Lucerne - Appenzell and back in 1 day means 6 hrs in trains.

As to the itinerary:
Zurich - Appenzell - Rapperswil - Lucerne - Interlaken - Gstaad - Montreux - Brig - Zurich would probably make more sense.

Thank you guyss... by we i mean there are no kids only adults.. i knw theres no downtime but we can always alter the itinerary once thrre depending on the weather n other conditions... so just wanted a rough plan to stick to.

yes our reservations are done ..thts wat is mkng it difficult to change the route :(

Lucerne to appenzell 6 hrs is too much... u think we can visit appenzell on a day trip from zurich on the first day... and keep Rhine falls on the last day? Will that make more sense?

Also can we hike to bachalpsee after visiting jungfrau?? Can both be done on the same day?

Count at least 3 hrs for the Bachalpsee hike.
The train ride from Jungfraujoch to Grindelwald lasts 1 3/4 hrs, the walk to the First gondola station 1/4 hrs, the gondola ride to First 1/2 hr OW and the train ride from Grindelwald to Interlaken West 3/4 hrs.
That means about 7 hrs from Jungfraujoch via Bachalpsee up to Interlaken.
If you leave Interlaken Ost at 6.35am, you will arrive at Jungfraujoch at 9am.
You must then leave Jungfraujoch not later than 11.00. otherwise you will miss the last gondola from First back to Grindelwald. You would then arrive back at Interlaken at 18.24

Thank you neckverd... like u mentioned Brig would be an ideal base to explore zermatt... i am considering brig as an option. As i also wanted to see verzasca valley.

But when i googled... brig to locarno.. the train takes us thru domosdola or milan.. is there any other way to get from brig to locarno or do we have to pass through italy?