(a) In general. With respect to gifts made prior to January 1, 1982, the marital deduction is allowable with respect to any transfer by a donor to the donor's spouse only to the extent that the transfer is shown to represent a gift of property that was not, at the time of the gift, held as community property, as defined in paragraph (b) of this section. The burden of establishing the extent to which a transfer represents a gift of property not so held rests upon the donor.

(b) Definition of “community property.” (1) For the purpose of paragraph (a) of this section, the term “community property” is considered to include—

(i) Any property held by the donor and his spouse as community property under the law of any State, Territory, or possession of the United States, or of any foreign country, except property in which the donee spouse had at the time of the gift merely an expectant interest. The donee spouse is regarded as having, at any particular time, merely an expectant interest in property held at that time by the donor and herself as community property under the law of any State, Territory, or possession of the United States, or of any foreign country, if, in case such property were transferred by gift into the separate property of the donee spouse, the entire value of such property (and not merely one-half of it), would be treated as the amount of the gift.

(ii) Separate property acquired by the donor as a result of a “conversion”, after December 31, 1941, of property held by him and the donee spouse as community property under the law of any State, Territory, or possession of the United States, or of any foreign country (except such property in which the donee spouse had at the time of the “conversion” merely an expectant interest), into their separate property, subject to the limitation with respect to value contained in subparagraph (5) of this paragraph.

(iii) Property acquired by the donor in exchange (by one exchange or a series of exchanges) for separate property resulting from such “conversion.”

(2) The characteristics of property which acquired a noncommunity instead of a community status by reason of an agreement (whether antenuptial or post-nuptial) are such that section 2523(f) classifies the property as community property of the donor and his spouse in the computation of the marital deduction. In distinguishing property which thus acquired a noncommunity status from property which acquired such a status solely by operation of the community property law, section 2523(f) refers to the former category of property as “separate property” acquired as a result of a “conversion” of “property held as such community property.” As used in section 2523(f) the phrase “property held as such community property” is used to denote the body of property comprehended within the community property system; the expression “separate property” includes any noncommunity property, whether held in joint tenancy, tenancy by the entirety, tenancy in common, or otherwise; and the term “conversion” includes any transaction or agreement which transforms property from a community status into a noncommunity status.

(3) The separate property which section 2523(f) classifies as community property is not limited to that which was in existence at the time of the conversion. The following are illustrative of the scope of section 2523(f):

(i) A partition of community property between husband and wife, whereby a portion of the property became the separate property of each, is a conversion of community property.

(ii) A transfer of community property into some other form of coownership, such as a joint tenancy, is a conversion of the property.

(iii) An agreement (whether made before or after marriage) that future earnings and gains which would otherwise be community property shall be shared by the spouses as separate property effects a conversion of such earnings and gains.

(iv) A change in the form of ownership of property which causes future rentals, which would otherwise have been acquired as community property, to be acquired as separate property effects a conversion of the rentals.

(4) The rules of section 2523(f) are applicable, however, only if the conversion took place after December 31, 1941, and only to the extent stated in this section.

(5) If the value of the separate property acquired by the donor as a result of a conversion did not exceed the value of the separate property thus acquired by the donee spouse, the entire separate property thus acquired by the donor is to be considered, for the purposes of this section, as held by him and the donee spouse as community property. If the value (at the time of conversion) of the separate property so acquired by the donor exceeded the value (at that time) of the separate property so acquired by the donee spouse, only a part of the separate property so acquired by the donor (and only the same fractional part of property acquired by him in exchange for such separate property) is to be considered, for purposes of this section, as held by him and the donee spouse as community property. The part of such separate property (or property acquired in exchange for it) which is considered as so held is the same proportion of it which the value (at the time of the conversion) of the separate property so acquired by the donee spouse is of the value (at that time) of the separate property so acquired by the donor. The following example illustrates the application of the provisions of this paragraph: