The IRS addresses this directly in IRM

Definition of "Complete Liquidation"
  1. "Complete liquidation" is a term not defined by the Code. The regulations under §332 suggest that the status of liquidation exists when the corporation ceases to be a going concern and its activities are merely for the purpose of winding up its affairs, paying its debts, and distributing any remaining balance to its shareholders. The Tax Court applies a three-pronged test to determine whether a complete liquidation has taken place (see Joseph Olmstead v. Commissioner T.C. Memo 1984-381):
    • Was there a manifest intent to liquidate?
    • Was there a continuing purpose to terminate corporate affairs and dissolve?
    • Were the corporate activities directed and confined to that purpose?
  2. Dissolution under state law or lack thereof will not be controlling for federal tax purposes. Intent coupled with actual distributions to the shareholders are the usual determining elements.
  3. IRC section 346(a) allows for a series of distributions pursuant to a plan of liquidation to be treated as being part of a complete liquidation. If the plan is not formal or is ambiguous, there may be uncertainty as to which distributions are made pursuant to the plan. Distributions made before there is evidence to support an intention to liquidate should be taxable as dividends (ordinary income to a shareholder).
  4. The U.S. Tax Court's decision in Pittsburgh Realty Investment Trust v. Commissioner, 67 T.C. 260, 1976, shed some light on a corporate liquidation. The Court stated that:
    1. The determination as to whether and/or when a corporation has liquidated is a question of fact. Proof of a distribution in complete liquidation not only depends on an intent to liquidate but also requires acts which demonstrate and effect that intent.
    2. A corporation in existence during any portion of a taxable year is required to make a return. If a corporation was not in existence throughout an annual accounting period (either calendar year or fiscal year), the corporation is required to make a return for that fractional part of a year during which it was in existence. A corporation is not in existence after it ceases business and dissolves, retaining no assets, whether or not under State law it may thereafter be treated as continuing as a corporation for certain limited purposes connected with winding up its affairs, such as for the purposes of suing and being sued. If the corporation has valuable claims for which it will bring suit during this period, it has retained assets and therefore continues to exist. A corporation does not go out of existence if it is turned over to receivers or trustees who continue to operate it.