Chapter 5 - Stereochemistry at Tetrahedral Centers (McMurry) Questions With Explanations Of Answers.

Our left and right hands are not identical to each other, rather, they are... - correct answer mirror images. Handedness is important in organic and biological chemistry, where it arises primarily as a consequence of the tetrahedral stereochemistry of... - correct answer sp3-hybridized carbon atoms. (5.1 Enantiomers and the Tetrahedral Carbon) - correct answer Molecules that are not identical to their mirror images are kinds of stereoisomers called... - correct answer enantiomers (from Greek "enantio-" meaning "opposite", and "-mer" denoting related kinds of molecules). Enantiomers result whenever a tetrahedral carbon is bonded to... - correct answer four different substituents (one need not be H). Lactic acid exists as a pair of enantiomers that are called... - correct answer (+)-lactic acid & (-)-lactic acid. Both enantiomers of lactic acid are found in sour milk, but only the (+) enantiomer occurs in... - correct answer muscle tissue. Regardless of how the molecules are oriented, enantiomers are never... - correct answer superimposable. (meaning, able to be placed over another) (5.2 The Reason for Handedness in Molecules: Chirality) - correct answer A molecule that is not identical to its mirror image is considered to be... - correct answer chiral. (from Greek "chir-" meaning "hand" and "-al" denoting to "pertaining to") Chiral molecules and their enantiomers are never... - correct answer superimposable. A molecule is not chiral if it has a... - correct answer plane of symmetry. (plane that cuts through the middle of a molecule to give equal halves) A molecule that has a plane of symmetry in any conformation must be identical to its mirror image and hence must be... - correct answer achiral. Propanoic acid, CH3CH2CO2H, has a plane of symmetry and is thus... - correct answer achiral. Lactic acid, CH3CH(OH)CO2H, has no plane of symmetry and is thus... - correct answer chiral. (with two enantiomers) The cause of chirality is due to the presence of a tetrahedral carbon atom bonded to four different groups—the carbon is known as... - correct answer the "chirality center". The terms: stereocenter, asymmetric center, and stereogenic center all refer to... - correct answer chirality centers. Carbons in —CH2—, —CH3, C=O, C=C, and C(triple bond)C groups can not be chirality centers, because... - correct answer they cannot be bonded to four different substituents. A substituted carbon atom in a cycloalkane ring can be a chirality center if... - correct answer the two paths along the ring, in opposite directions, are different. Carbons of a benzene ring cannot be chirality centers because they have... - correct answer a plane of symmetry. Although benzene rings cannot be chiral themselves, they can be... - correct answer one of the four substituents connected to a chiral carbon. (5.3 Optical Activity) - correct answer The study of chirality originated in the 19th century by a French physicist (Jean-Baptiste Biot) who was studying... - correct answer plane-polarized light. A beam of light consists of... - correct answer electromagnetic waves. The electromagnetic waves of light oscillate in an infinite number of planes at right angles to... - correct answer the direction of travel. When a beam of ordinary light passes through a device called a "polarizer", the only light waves that pass through are the ones that are oscillating in a... - correct answer single plane. The light passing through a polarizer is said to be... - correct answer "plane-polarized". When a beam of plane-polarized light passes through a solution of certain organic molecules, the plane of polarization is... - correct answer rotated through an angle, α. Organic molecules that are able to rotate the plane of polarization are said to be... - correct answer "optically active". The angle of rotation of the polarization plane can be measured with an instrument called a... - correct answer polarimeter. The plane-polarized light goes through a sample tube containing optically active organic molecules, and then goes through a second polarizer called the... - correct answer analyzer. The analyzer of a polarimeter is rotated until... - correct answer the rotated plane-polarized light passes through it. Optically active molecules that rotate polarized light to the left (counter-clockwise), from the vantage point of the observer looking directly at the analyzer, are said to be... - correct answer levorotatory. ( |ˌlēvəˈrōtəˌtôrē|) ("levo-" means "to the left") Optically active molecules that rotate polarized light to the right, are said to be... - correct answer dextrorotatory. (|ˌdekstrəˈrōtəˌtôrē|) ("dextro-" means "to the right") By convention, levorotatory (left-rotating) molecules are depicted with a... - correct answer minus sign (-). Dextrorotatory (right-rotating) molecules are depicted with a... - correct answer plus sign (+). The extent of rotation observed in a polarimetry experiment depends on the concentration of... - correct answer optically active molecules. Rotation is also directly related to... - correct answer pathlength. To express optical rotations in a meaningful way so that comparisons can be made, a property of chiral chemical compounds is used—known as... - correct answer specific rotation, [α]D. The specific rotation values ([α]D) for (+) and (-)-lactic acid are +3.82 and -3.82 respectively, indicating that the two enantiomers rotate plane-polarized light to exactly the same extent, but... - correct answer in opposite directions. (5.4 Pasteur's Discovery of Enantiomers) - correct answer Pasteur separated sodium ammonium tartrate crystals into two distinct piles, which had two distinct geometric forms, known as... - correct answer enantiomers. The original sample of crystals, before being separated, had a 50:50 ratio of levorotatory and dextrorotatory crystals, and was therefore optically... - correct answer inactive. Enantiomers have identical physical properties, such as melting point and boiling point, but differ in which direction their solutions rotate plane-polarized light; therefore, enantiomers are also known as optical... - correct answer isomers. (5.5 Sequence Rules for Specifying Configuration) - correct answer The three-dimensional arrangement of substituents at a chirality center is known as the molecule's... - correct answer configuration. The Cahn-Ingold-Prelog rules, or CIP rules, are a set of rules used to name... - correct answer stereoisomers of a molecule. Using CIP rules, the four atoms directly attached to the chirality center are ranked according to... - correct answer atomic number. The atom, out of the possible four, with the highest atomic number is given a ranking of... - correct answer 1. Using CIP rules, if a decision can't be reached by ranking the first atoms in the substituent, look at the... - correct answer next atoms distal to the chirality center. When ranking substituents, multiple-bonded atoms are equivalent to... - correct answer the same number of single-bonded atoms. For example, when using CIP rules the double bonded carbon to oxygen in an aldehyde group would be bonded to... - correct answer two oxygens. After ranking the four groups attached to the chiral carbon, we describe the stereochemical configuration around the carbon by orienting the molecules so that the lowest ranking group (4) is... - correct answer pointing directly back. If a curved arrow can be drawn from the first to the second and to the third substituent in the clockwise direction, we say that the chirality center has the... - correct answer R configuration. (from Latin "rectus", meaning "right") If an arrow can be drawn from 1 to 2 to 3 in the counterclockwise direction, the chirality center has the... - correct answer S configuration (from Latin "sinister", meaning "left") R, S configuration is not related to... - correct answer the sign of optical rotation, (+) or (-). In regards to optical rotation, a molecule having an S configuration can be either... - correct answer levorotatory (-) or dextrorotatory (+). (5.6 Diastereomers) - correct answer A molecule with "n" chirality centers can have up to... - correct answer 2^n stereoisomers. Stereoisomers that are not mirror images of each other are known as... - correct answer diastereomers. Enantiomers have oposite configurations at... - correct answer ALL chirality centers. Diastereomers have opposite configurations at... - correct answer SOME chirality centers, and the same configuration at others. Most biological molecules are chiral, and usually only... - correct answer one stereoisomer is found in nature.