list conversion

[Z. Huang]

Given a list ("first" "second" "third"). I'd to convert it to a 
a new list: 
   (("" . "first")
    ("" . "second")
    ("" . "third"))     

The following lisp code was intended for this purpose, but not working. It
looks that I missed some very basic stuff (I rarely code in lisp). Can
anyone point out what is wrong? Thanks in advance. 

(defun list-conversion (arg)
  (let ((l arg) (new-list ()))
    (while l
      (append new-list (list "" . (car l))))
      (setq l (cdr l))))