or disrotatory electrocyclic reactions." In other words, a chemical reaction is torquoselective if the groups of atoms that hang from a ring of atoms are more likely to have rotated in a particular direction during the reaction (instead of being equally likely to rotate in both possible directions.) Torquoselectivity is different from the normal diastereoselectivity of pericyclic reactions. Instead it is more selectivity beyond the Woodward–Hoffmann rules. The name comes from the idea that the substituents in an electrocyclization appear to rotate during the reaction. The reaction produces a single product because only one direction of rotation was allowed (that is, the direction of rotation on the substituents was favored). The concept was originally developed by Kendall N. Houk.
When a chemical reaction closes a ring, its torquoselectivity is the same as enantioselectivity. A single enantiomer of a cyclization product is formed from the selective ring closure of the starting material. In a typical electrocyclic ring closing, selection for either conrotatory or disrotatory reactions modes still produces two enantiomers. Torquoselectivity is a discrimination "between" these possible enantiomers that requires asymmetric induction.
Torquoselectivity also happens in selective electrocyclic reactions that break open rings. The different directions of rotation produce distinct structural isomers. In these cases, steric strain is often the driving force for the selectivity. Studies have shown that the selectivity can also be changed by the presence of electron donating and electron withdrawing groups.
Torquoselectivity can also apply to other mechanisms, including chiral Lewis acid catalysts, induction by neighboring stereocenters (in which case the torquoselectivity is a case of diastereoselectivity), and axial-to-tetrahedral chirality transfer. An example of axial-to-tetrahedral chirality transfer is shown below for the torquoselective Nazarov cyclization reaction of a chiral allenyl vinyl ketone.
2011 Pan American Games
The 16th Pan American Games were held in 2011 in Guadalajara, Mexico. Over 6,000 athletes from 42 countries competed in 36 sports.
William Kidd
Captain Kidd, or, by his real name, "William Kidd", (c. 1645 – 23 May 1701) was a Scottish pirate and sailor. It is heard that he buried a treasure chest on a deserted island. The chest had a lot of gold and jewels in it. He was found guilty of murder and was executed by hanging at 'Execution Dock', Wapping, in London on 23 May 1701.
Gripper
A gripper is something that grips things or makes it easier to grip things. It may refer to:
Jeff Kent
Jeffrey Franklin Kent (born March 7, 1968) was an American baseball player. He played second base. He played for six different teams, including the New York Mets, San Francisco Giants, and Los Angeles Dodgers. He was a five-time All-Star, and the 2000 National League MVP. In his career, he batted .290, with 2,461 hits, 377 home runs and 1,518 RBIs. He has more home runs than any other second baseman. He also drove in 90 or more batters in nine straight seasons.
Kent was from Bellflower, California and went to high school in Huntington Beach.
Angelshark
An angelshark is a species of cartilaginous fish in the genus Squatina. They have flattened bodies and wide pectoral fins, which make them look similar to rays. Twenty-three species are known.
The genus is the only one in its family, Squatinidae, and order Squatiniformes. They are worldwide in temperate and tropical seas. Most species are in shallow temperate or tropical seas, but one species is found in deeper water, down to 1,300 metres. Angelsharks are specialised for a kind of predation which is unusual for sharks.
They are ambush predators. They have extensible jaws with long, needle-like teeth. They quickly snap upwards to capture prey. They bury themselves in sand or mud lying in wait for their prey, which includes fish, crustaceans, and many different types of mollusks.
The front part of the angel sharks' bodies are wide and flattened, but the back part is more muscular. The eyes and spiracles are on the top, and the five gill slits are on its back. Both the pectoral fins and the pelvic fins are large and are held horizontally. There are two dorsal fins, no anal fin. Unusually for sharks, the lower lobe of the caudal fin is longer than the upper lobe. Most types of angel sharks grow to a length of about 1.5 metres: the Japanese angelshark reaches two metres. They are ovoviviparous, and can have up to 13 pups at a time.
Although angelsharks are bottom dwellers and appear harmless, they can give painful bites if provoked, due to their powerful jaws and sharp teeth. Angelsharks may bite if a diver approaches the head or grabs the tail.
Goblin shark
The goblin shark ("Mitsukurina owstoni") is a rare, poorly-known species of deep-sea shark. Sometimes called a "living fossil", it is the only living species in the family Mitsukurinidae.
The Goblin shark can be easily identified by its long, flattened snout. Males can reach up to lengths of 12.6 feet (3.8 meters), and females can reach up to lengths of 12.2 feet (3.7 meters). The heaviest Goblin shark found weighed 210 kg (460 pounds).
The Goblin shark is a bottom-dwelling shark, being found in waters as deep as 4265 feet (1,300 meters). It has been found in the Atlantic, Indian, and Pacific Ocean.
The Goblin shark can be easily identified by its long, flattened snout. It has a noticeably long head, tiny eyes and five short gill openings. The mouth is large and parabolic in shape. Its body is soft and flabby. This shark has a long caudal fin without a ventral lobe. The pectoral fins are short and wide, and the two dorsal fins are small, round and equal in size. The anal fin is round and smaller than the dorsal fins, while the pelvic fins are larger than the dorsals. The Goblin shark has a long extendable jaw, with long, thin teeth. The shape of its body shows that the Goblin shark is a slow moving species of shark.
Living Goblin sharks are a pinkish-white color with bluish fins. Specimens fade and become a brownish color when preserved in alcohol.
Goblin sharks have 26 long, thin, spike-like teeth on their upper jaw and 24 on their lower jaw. They have three rows of front teeth on each side of both jaws. The teeth in the front upper jaw are separated from the smaller upper side teeth by a gap.
Mature male Goblin sharks have been found to reach lengths ranching from 8.66 to 12.6 feet (2.6 to 3.8 meters) long. Mature females have been found to reach lengths ranging from 11 to 12.2 feet (3.4 to 3.7 meters). The size at birth is not known, but the smallest specimen found was 3.51 feet (1.07 meters) long. The heaviest Goblin shark found weighed 210 kg (460 pounds), and was 3.8 metres (12 feet) long.
This species of deep-sea shark is thought to be widely distributed. Specimens have been seen in the Atlantic, off the coast of Guyana, Surinam, French Guiana, France, Madeira, Senegal, Portugal, and the Gulf of Guinea. It has also been reported in the western Pacific off Japan, Australia and New Zealand. In the Indian Ocean it is found off South Africa and Mozambique. It was recently recorded in the U.S.A near San Clemente Island off the coast of California, as well as in the northern Gulf of Mexico, south of Pascagoula, Mississippi.
The Goblin shark is a bottom-dwelling shark that is rarely seen at the surface or in shallow coastal waters. This species is found along the outer continental shelves, upper slopes, and off seamounts. Most specimens have been observed near continental slopes, between 885 and 3149 feet (270 and 960 meters) deep. It has been found in waters up to 4265 feet (1,300 meters) deep, and in waters as shallow as 311 to 449 feet (95 to 137 meters). Records show that the Goblin shark could also be an oceanic species.