I have problem with sending ajax request

I have problem with sending ajax request

Hello,

I wrote a login form where on submit the user is supposed to logged in, but it is not working. please let me know where is the error is,
This is the form

                         <form id ="loginform_" action="">
                             <a href=""id="slidedownclose">X</a>
                              <h2> Login Form</h2>
                             Username:<input type="text" id="uname" name="user_name"  /><br/><br/>
                             Password:<input type="password" id="password" name="password" /><br/><br/>
                            <input type ="submit" id ="log"  class="logclass" value="log in"/><br/><br/>
                            <a id ="lost_password" href ="/frontend_dev.php/forgotpassword">Forgot Password </a>
                            </form>

this is the jquery code


$(document).ready(function()
{

$("#loginform_").validate({
                               
                rules: {
                    user_name: "required",
                                        password: "required"
                }


            });
$(".logclass").click(function()
                    {
                       
                        var data =$("#loginform_").serialize();
                        $.ajax({
                        type: "POST",
                        url: "/frontend_dev.php/login/new",
                        data: data,
                        success: function(){
                         alert('success');
                         window.location.replace("/frontend_dev.php/user");
                        },
                        error: function(){
                         alert(data);
                        }
                        });
                    });

                     });

Thanks in advance.