Use .htaccess to redirect to subfolder -

i have following documentroot structure on webserver:

folder1 folder2 

i can access of them in standard way

my.ip.address.here/folder1 my.ip.address.here/folder2 

i want redirect request website doesn't have particular folder specified 1 default folder, namely 'folder1'. example, if type in browser my.ip.address.here, redirects me 'my.ip.address.here/folder1'. have .htaccess file located inside documentroot folder following contents:

rewriteengine on rewriterule ^$ /folder1 [r=301, l] 

when run website in browser following eror:

internal server error server encountered internal error or misconfiguration , unable complete request.  please contact server administrator, webmaster@localhost , inform them of time error occurred, , might have done may have caused error.  more information error may available in server error log. 

what wrong configuration? in advance!

if simple want redirect internally or not / folder2 of these rules would.

redirect 301 using rule:

rewriterule ^$ /folder2 [r=301,l] 

internally url not change:

rewriterule ^$ /folder2 [l] 

use 302 if want temporary redirect , 301 permanent redirect.