Oct 12 (Reuters) - A former Portsmouth, Virginia, police officer was sentenced on Wednesday to 2-1/2 years in prison for the shooting death of an unarmed black teenager last year, a court spokesman said.

The ex-officer, Stephen Rankin, 36, was convicted of voluntary manslaughter in August for shooting William Chapman II, 18, while investigating a shoplifting report at a Walmart store.

Portsmouth Circuit Court Judge Johnny Morrison denied a request by Rankin's lawyer that he remain free while his conviction is appealed, the spokesman said in a telephone call.

Rankin, who is white, was fired by the Portsmouth police department after his grand jury indictment. Prosecutors argued that Rankin had killed Chapman in April 2015 in what had amounted to little more than a parking lot fistfight in Portsmouth, about 175 miles south of Washington.

The sentencing came amid a roiling U.S. debate over police use of deadly force, especially against African-Americans. A Washington Post database showed that 754 people have been fatally shot by police this year, with 24 percent of them black.

Rankin is among 26 officers to be convicted of murder or manslaughter for an on-duty shooting out of 77 charged since 2005, Phillip Stinson, an associate professor of criminal justice at Ohio's Bowling Green State University, said in a telephone call.

Twenty-nine of the charges were leveled in the last two years alone, but Stinson said the numbers were too small to indicate a trend of officers being charged.

Rankin had shot and killed an unarmed man in 2011 while responding to a burglary call. No charges were filed over that shooting, and Rankin won a related civil trial.

(Reporting by Ian Simpson in Washington; Editing by Richard Chang)

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