Final answer:
The Singer Building was demolished in 1968 to make way for 1 Liberty Plaza, and it was the tallest building ever destroyed until 9/11. Its loss marked a significant event in the history of architectural preservation.
Step-by-step explanation:
The building that was demolished in 1968, which became the site for 1 Liberty Plaza and was the tallest building ever destroyed until the events of 9/11, is known as the Singer Building. The Singer Building, along with the adjacent City Investing Building, was considered a significant loss to architectural heritage and was one of the early failures of the building preservation movement. Although many iconic structures like the Seagram Building had defined the New York skyline in their time, the destruction of the Singer Building stands out as a landmark moment in the history of urban development and historic preservation.