If you face problem to access your google chat from pidgin when you are behind proxy; please do the following settings:
1. Go to Tools > Manage Accounts > Modify Account
2. Go to Advance Tab. Uncheck “Require SSL/TLS” & “Allow plaintext auth over unencrypted streams”. Please check “Force old (port 5223) SSL”
3. Change the connect port to 443
4. Change connect server to “talk.google.com”
5. Go to proxy tab. Select HTTP and put your proxy related information.