The Battle of Gettysburg was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania, by Union and Confederate forces during the American Civil War. The battle involved the largest number of casualties of the entire war and is described as the war's turning point. Union Maj. Gen. George Meade's Army of the Potomac defeated attacks by Confederate Gen. Robert E. Lee's Army of Northern Virginia, halting Lee's invasion of the North. After his success at Chancellorsville in Virginia in May 1863, Lee led his army through the Shenandoah Valley to begin his second invasion of the North—the Gettysburg Campaign. With his army in high spirits, Lee intended to shift the focus of the summer campaign from war-ravaged northern Virginia and hoped to influence Northern politicians to give up their prosecution of the war by penetrating as far as Harrisburg, Pennsylvania, or Philadelphia. Prodded by President Abraham Lincoln, Maj. Gen. Joseph Hooker moved his army in pursuit, but was relieved of command just three days before the battle and replaced by Meade.

Elements of the two armies collided at Gettysburg on July 1, 1863, as Lee urgently concentrated his forces there, his objective being to engage the Union army and destroy it. Low ridges to the northwest of town were defended by a Union cavalry division under Brig. Gen. John Buford, soon reinforced with two corps of Union infantry. However, two large Confederate corps assaulted them from the northwest and north, collapsing the hastily developed Union lines, sending the defenders retreating through the streets of the town to the hills just to the south. On the second day of battle, most of both armies had assembled; the Union line was laid out in a defensive formation resembling a fishhook. In the late afternoon of July 2, Lee launched a heavy assault on the Union left flank, fierce fighting raged at Little Round Top, the Wheatfield, Devil's Den, the Peach Orchard. On the Union right, Confederate demonstrations escalated into full-scale assaults on Culp's Hill and Cemetery Hill. All across the battlefield, despite significant losses, the Union defenders held their lines.

On the third day of battle, fighting resumed on Culp's Hill, cavalry battles raged to the east and south, but the main event was a dramatic infantry assault by 12,500 Confederates against the center of the Union line on Cemetery Ridge, known as Pickett's Charge. The charge was repulsed at great loss to the Confederate army. Lee led his army on a torturous retreat back to Virginia. Between 46,000 and 51,000 soldiers from both armies were casualties in the three-day battle, the most costly in US history. On November 19, President Lincoln used the dedication ceremony for the Gettysburg National Cemetery to honor the fallen Union soldiers and redefine the purpose of the war in his historic Gettysburg Address. Shortly after the Army of Northern Virginia won a major victory over the Army of the Potomac at the Battle of Chancellorsville, Robert E. Lee decided upon a second invasion of the North; such a move would upset the Union's plans for the summer campaigning season and reduce the pressure on the besieged Confederate garrison at Vicksburg.

The invasion would allow the Confederates to live off the bounty of the rich Northern farms while giving war-ravaged Virginia a much-needed rest. In addition, Lee's 72,000-man army could threaten Philadelphia and Washington, strengthen the growing peace movement in the North. Thus, on June 3, Lee's army began to shift northward from Virginia. Following the death of Thomas J. "Stonewall" Jackson, Lee reorganized his two large corps into three new corps, commanded by Lt. Gen. James Longstreet, Lt. Gen. Richard S. Ewell, Lt. Gen. A. P. Hill; the Cavalry Division remained under the command of Maj. Gen. J. E. B. Stuart; the Union Army of the Potomac, under Maj. Gen. Joseph Hooker, consisted of seven infantry corps, a cavalry corps, an Artillery Reserve, for a combined strength of more than 100,000 men; the first major action of the campaign took place on June 9 between cavalry forces at Brandy Station, near Culpeper, Virginia. The 9,500 Confederate cavalrymen under Stuart were surprised by Maj. Gen. Alfred Pleasonton's combined arms force of two cavalry divisions and 3,000 infantry, but Stuart repulsed the Union attack.

The inconclusive battle, the largest predominantly cavalry engagement of the war, proved for the first time that the Union horse soldier was equal to his Southern counterpart. By mid-June, the Army of Northern Virginia was poised to enter Maryland. After defeating the Union garrisons at Winchester and Martinsburg, Ewell's Second Corps began crossing the river on June 15. Hill's and Longstreet's corps followed on June 24 and 25. Hooker's army pursued, keeping between Washington, D. C. and Lee's army. The Union army crossed the Potomac from June 25 to 27. Lee gave strict orders for his army to minimize any negative impacts on the civilian population. Food and other supplies were not seized outright, although quartermasters reimbursing Northern farmers and merchants with Confederate money were not well received. Various towns, most notably York, were required to pay indemnities in lieu of supplies, under threat of destruction. During the invasion, the Confederates seized some 40 northern African Americans.

A few of them were escaped fugitive slaves.

The asymmetric addition of alkynylzinc compounds to aldehydes is an example of a Nef synthesis, a chemical reaction whereby a chiral propargyl alcohol is prepared from a terminal alkyne and an aldehyde. This alkynylation reaction is enantioselective and involves an alkynylzinc reagent rather than the sodium acetylide used by John Ulric Nef in his 1899 report of the synthetic approach. Propargyl alcohols are versatile precursors for the chirally-selective synthesis of natural products and pharmaceutical agents, making this asymmetric addition reaction of alkynylzinc compounds useful. For example, Erick Carreira used this approach in a total synthesis of the marine natural product leucascandrolide A, a bioactive metabolite of the calcareous sponge Leucascandra caveolata with cytotoxic and antifungal properties isolated in 1996. Various chiral ligands have been studied for use in this reaction; the acidity of the terminal alkynyl proton allows the alkynylzinc compound to be generated in situ from the appropriate alkyne with an alkylzinc reagent or zinc triflate, Zn2.

The first example of catalytic asymmetric addition of alkynylzinc compounds to aldehydes was reported by Kenso Soai and co-workers in 1990. In their experiments, chiral amino alcohols and amines were used as ligands, the alkynylzinc reagent was prepared from reaction of alkyne with diethylzinc. Yields were high but the resulting enantiomeric excesses were poor, the greatest achieved being only 34% with 5 mol% ligand loading. Carreira and co-workers achieved higher enantiomeric excesses using stoichiometric amounts of the -enantiomer of N-methylephedrine at room temperature with a broad range of aldehydes, generating the alkynylzinc compound using Zn2

This list lists achievements and distinctions of various first ladies of the United States. It includes distinctions achieved in post-first lady service. There have been forty-five first ladyships; this discrepancy exists because some presidents remarried while in office and some were not married so had no official first lady. Note that first ladies not recognized by the National First Ladies' Library listing include Martha Jefferson Randolph, Emily Donelson, Sarah Yorke Jackson, Angelica Van Buren, Priscilla Tyler, Mary McElroy, Rose Cleveland, Mary McKee, Margaret Woodrow Wilson. First first lady. First first lady to have a U. S. stamp honoring her. First first lady to have a U. S. military ship named in her honor. First first lady to outlive her husband. First first lady to live in the White House. First first lady to be the mother of a president. First first lady to have been a second lady. First first lady to predecease her husband. First first lady to give birth to a child in the White House. First first lady to not be the sitting president's wife.

She was his daughter. First first lady given an honorary seat on the floor of Congress. First first lady to respond to a telegraph message. First first lady to die at over eighty years old. First first lady born outside of the United States. First first lady to have both houses of the United States Congress adjourn in mourning on the day of her funeral. First first lady to be the daughter-in-law of another first lady. First first lady to have been born in the 19th century. First first lady to have a post first ladyship of 50 years. First first lady to be widowed while holding the title. First first lady to be granted by law a pension as a president's widow. First first lady to be the grandmother of a president. First first lady to die in the White House. First first lady to travel with the president as an official member of the presidential party. First first lady to have been born in the 19th century. First first lady to marry a president, in office at the time of the wedding. First first lady to be photographed while in office.

First first lady to serve as a secretary to the president. First first lady to have no children. First first lady to host an annual Thanksgiving dinner at the White House. First first lady to hold séances in the White House. First first lady recorded on film. First first lady to write her memoirs. First first lady to earn a college degree. First first lady to host an Easter Egg roll on the White House lawn. First first lady to marry in the White House. First first lady to have a child in the White House. First first lady to preside at two nonconsecutive administrations. First first lady to remarry after widowing. First first lady to raise a Christmas tree in the White House. First first lady to be the granddaughter-in-law of another first lady. First first lady to travel abroad. First first lady to drive a car. First first lady to ride in her husband’s inaugural parade. First first lady to support women's suffrage. First first lady to publish her memoirs. First first lady to smoke cigarettes. First first lady to lobby for safety standards in federal workplaces.

First first lady to unofficially assume presidential functions. First first lady to vote. First first lady to fly in an airplane. First first lady to operate a movie camera. First first lady to own a radio. First first lady to invite movie stars to the White House. First first lady to earn a four-year undergraduate degree. First first lady to speak in sound newsreels. First first lady to make regular nationwide radio broadcasts. First first lady to hold regular press conferences. First first lady to write a monthly magazine column. First first lady to host a weekly radio show. First first lady to speak at a national party convention. First first lady to be depicted as part of a presidential memorial. First first lady to be the niece of a former president. First first lady to initiate Halloween decorations to be put up in the White House. First first lady to be born in the 20th century. First first lady to hire a press secretary. First first lady to hire a White House curator. First first lady to win an Emmy Award.

First first lady to be Catholic. First first lady to become a millionaire in her own right. First first lady to enter a combat zone. First first lady to travel to the Soviet Union. First first lady to wear pants in public. First first lady to address a Republican National Convention. First first lady to admit having a drinking problem. First first lady to keep her own office in the East Wing. First first lady invited to address the United Nations General Assembly. First first lady married to a divorcée. First first lady to live to see a son become president. First first lady to earn a postgraduate degree. First first lady to have her own professional career up to the time of entering the White House. First first lady with an office in the West Wing. First first lady to win a Grammy Award. First first lady to be subpoenaed to testify before a federal grand jury. First first lady to win elected office. First first lady to march in an LGBT pride parade. First first lady to run for president. First first lady to have served in the cabinet and be in the presidential line of succession, as secretary of state.

First first lady to be nominated for president by a major U. S. political party. First first lady to have won the popular vote in the United States presidential elections. First first lady to give bi