Sec. 503. Requirements for Exemption.
(a) Denial of Exemption to Organizations Engaged in Prohibited Transactions
  (1) General Rule An organization described in section 501(c)(3) which is subject to the provisions of this section shall not be exempt from taxation under section 501(a) if it has engaged in a prohibited transaction after July1, 1950; and an organization described in section 401(a) which is subject to the provisions of this section shall not be exempt from taxation under section 501(a) if it has engaged in a prohibited transaction after March 1, 1954
  (2) Taxable Years affected
(b) Organizations to Which Section Applies This section shall apply to an organization described in section 501(c)(3) or section 401(a) except
  (1) . . .
(c) Prohibited Transactions— For the purpose of this section, the term "prohibited Transaction" means any transaction in which an organization subject to the provisions of this section
  (1) lends any part of its income or corpus, without the receipt of adequate security and a reasonable rate of interest, to;
  (2) pays any compensation, in excess of a reasonable allowance for salaries or other compensation for personal services actually rendered, to;
  (3) makes any part of its services available on a preferential basis to;
  (4) makes any substantial purchase of securities or other property, for less than adequate consideration in money or money's worth, from;
  (5) sells any substantial part of its securities or other property, for less than adequate consideration in money or money's worth, to; or
  (6) engages in any other transaction which results in a substantial diversion of its income or corpus to; the creator of such organization (if a trust); a person who has made a substantial contribution to such organization; a member of the family (as defined in section 267(c)(4)) of an individual who is the creator of such trust or who has made a substantial contribution to such organization; or corporation controlled by such creator or person through the ownership, directly of indirectly, of 50 percent or more of the total combined voting power of all classes of stock entitled to vote of 50 percent or more of the total value of shares of all classes of stock of the corporation.
(g) Special Rules for Loans . . .