The Woodward–Hoffmann rules are a set of organic chemistry rules to predict the stereochemistry of pericyclic reactions. Pericyclic reactions are usually rearrangement reactions where the molecule is a ring (e.g. benzene ring). They were written by Robert Burns Woodward (a chemistry professor at Harvard University) and Roald Hoffmann (a chemistry professor at Cornell University). Hoffmann was awarded the 1981 Nobel Prize in Chemistry for this work, shared with Kenichi Fukui who developed a similar model. Woodward did not share the prize because he died two years before. Generally, the Nobel Prize is awarded only to living people. Woodward had already won a Nobel Prize in Chemistry for a different discovery.
A recent paper in the journal "Nature" describes how mechanical stress can be used to reshape chemical reaction pathways to lead to products that apparently violate Woodward–Hoffman rules.
Stereochemistry
Stereochemistry is the study of how molecules are affected by the way their atoms are arranged in space. It is also known as 3D chemistry as the word "stereo" means "three dimensional". Using stereochemistry, chemists can work out the relationships between different molecules that are made up from the same atoms. They can also study the effect on the physical or biological properties these relationships give molecules. When these relationships influence the reactivity of the molecules it is called dynamic stereochemistry.
In chemistry, some molecules have more than one isomer. This means that molecules can have different forms, even though all the forms made up of the same atoms. There are two kinds of isonomers. Constitutional isomers have the same atoms, but they are joined differently. Stereoisomers have the same atoms, they are joined the same way, but the atoms are arranged differently in space. An important part of stereochemistry is the study of chiral molecules. These molecules look almost identical, except that one molecule is the mirror image of the other.
In most chemical bonds, the atoms of a molecule free to move around without breaking the bonds. When a molecule has a double bond or a ring structure, the molecule can be sorted into different isomers. These are molecules with the same chemical structure but different forms.
The study of stereochemical problems covers the entire range of organic, inorganic, biological, physical and supramolecular chemistries.
Louis Pasteur was the first person to study stereochemistry. He observed in 1849 that salts of tartaric acid collected from wine-making equipment could rotate plane polarized light, but that salts from other sources did not. This property was the only difference between the two types of salt. It is due to optical isomerism. In 1874, Jacobus Henricus van 't Hoff and Joseph Le Bel discovered the difference was caused by the way that the atoms bonded to carbon in a tetrahedral (four faced) shape.
Stereochemistry was important in solving the thalidomide disaster in the 1960s. Thalidomide is a drug that was first produced in 1957 in Germany. Doctors used it to treat morning sickness in pregnant women. Later, the drug was shown to cause deformations in babies. One isomer of the drug was not dangerous, but the other caused serious genetic damage to the embryos. In the human body, thalidomide undergoes racemization: even if only one of the two stereoisomers enters a human body, the body changes some of it to other one. The thalidomide disaster caused governments to test drugs more carefully. Selected people take new drugs in an experiment (clinical trial) first before the drug is made available for public use. Thalidomide is now used as a therapy for leprosy. Women must use it with contraceptives to prevent pregnancy.
When an atom can have other atoms connect to it in more than one way, it is called a stereocenter. For example, if a carbon atom has four different groups attached to it, it becomes a stereocenter.
Cahn-Ingold-Prelog priority rules are part of a system for describing a molecule's stereochemistry. They rank the atoms around a stereocenter in a standard way. This allows the relative position of these atoms in the molecule to be described very clearly. A Fischer projection is a simplified way to show the stereochemistry around a stereocenter.
Cornel West
Cornel Ronald West (born June 2, 1953) is an American philosopher, author, critic, actor, and civil rights activist. He is a member of the Democratic Socialists of America. West is the Class of 1943 University Professor at Princeton University. He teaches in the Center for African American Studies and in the Department of Religion. West is known for his combination of political and moral insight and criticism and his contribution to the post-1960s civil rights movement. Much of West's work focuses on the role of race, gender, and class in American society and the means by which people act and react to their "radical conditionedness". West draws intellectual contributions from such diverse traditions as the African American Baptist Church, pragmatism and transcendentalism.
West was born in Tulsa, Oklahoma, and grew up in Sacramento, California, where his father was a general contractor for the Defense Department and his mother was a teacher and a principal. Irene B. West Elementary School, Elk Grove, California, is named for her. While West was a student, he marched in civil rights demonstrations. As the class president in his high school, West organized protests demanding black studies courses. He later wrote that, in his youth, he admired "the sincere black militancy of Malcolm X, the defiant rage of the Black Panther Party [...] and the livid black theology of James Cone."
In 1970, West graduated from John F. Kennedy High School. He enrolled at Harvard University and took classes from philosophers Robert Nozick and Stanley Cavell. In 1973, he graduated "magna cum laude" in Near Eastern Languages and Civilization. "Owing to my family, church, and the black social movements of the 1960s", he says, "I arrived at Harvard unashamed of my African, Christian, and militant de-colonized outlooks. More pointedly, I acknowledged and accented the empowerment of my black styles, mannerisms, and viewpoints, my Christian values of service, love, humility, and struggle, and my anti-colonial sense of self-determination for oppressed people and nations around the world."
In 1980, he earned a Ph.D. from Princeton, where he was influenced by Richard Rorty's pragmatism. The title of his dissertation was "Ethics, historicism and the Marxist tradition", which was later revised and published under the title "The Ethical Dimensions of Marxist Thought".
In his mid-20s, he returned to Harvard as a W. E. B. Du Bois Fellow before becoming an Assistant Professor at Union Theological Seminary in the City of New York. In 1985, he worked at Yale Divinity School in what eventually became a joint appointment in American Studies. While at Yale, he participated in campus protests for a clerical labor union and divestment from apartheid South Africa. He was arrested and jailed at one of the protests. As punishment, the University administration canceled his leave for Spring 1987, leading him to commute from Yale in New Haven, Connecticut, where he was teaching two classes, across the Atlantic Ocean to the University of Paris.
He then returned to Union and taught at Haverford College in Pennsylvania for one year before going to Princeton to become a Professor of Religion and Director of the Program in African-American Studies (1988–94). He worked with novelist Toni Morrison to improve the Princeton program.