syntax error missing operator in query expression

String typeoftrans = comboBox1_TransactionType.Text.ToString();
           
            String ondate = DateTime.Now.ToString();
            string desc = textBox2_Description.Text.ToString();
            string amnt = textBox3_Amount.Text.ToString();

          try
            {

                con.Open();
                string Sql = "insert into Account_Transactions(TransactionType,Description,Amount,OnDateTime) values('" +typeoftrans+ ",'" + desc + "','" + amnt + "','" + ondate + "')";

                OleDbCommand cmd1 = new OleDbCommand(Sql, con);

                int temp = cmd1.ExecuteNonQuery();
                if (temp > 0)
                {
                    MessageBox.Show("Transaction done!");
                }
                else
                    MessageBox.Show("error");
            }
            catch (Exception e2)
            {
                MessageBox.Show(e2.ToString());
            }
            finally
            {
                con.Close();
            }