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CHEM 261: CHAPTER 5 IMPORTANT TERMS
absolute configuration
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the three-dimensional structure of a chiral compound. the configuration is designated by R or S. the configuration is called absolute to distinguish it from a relative configuration
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achiral |
a molecule or object that contains an element (a plane or point) of symmetry
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cis-trans isomers
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result from not being able to rotate about a carbon-carbon bond. they are also called geometric isomers or E,Z isomers
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cis isomer
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the isomer with substituents on the same side of a cyclic structure, or the isomer with the hydrogens on the same side of a double bond
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trans isomer
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the isomer with substituents on the opposite sides of a cyclic structure or the isomer with the hydrogens on the opposite sides of a bond
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chiral |
has a nonsuperimposable mirror image
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asymmetric center
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an atom that is bonded to four different substituents
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enantiomers
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nonsuperimposable mirror-image molecules
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stereocenter (stereogenic center)
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an atom at which the interchange of two groups produces a stereoisomer
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perspective formula
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method of representing the spatial arrangement of groups bonded to an asymmetric center. two bonds are drawn in the plane of the paper; a solid wedge is used to depict a bond that projects out of the plane of the paper toward the viewer, and a hatched wedge is used to represent a bond that projects back from the paper away from the viewer
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fischer projection
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a method of representing the spatial arrangement of groups bonded to an asymmetric center. the asymmetric center is the point of intersection of two perpendicular lines; the horizontal lines represent bonds that project out of the plane of the paper toward the viewer, and the vertical lines represent bonds that project back from the plane of the paper away from the viewer
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R configuration
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after assigning relative priorities to the four groups bonded to an asymmetric center, if the lowest-priority group is on a vertical axis in a fischer projection (or pointing away from the viewer in a perspective formula), an arrow drawn from the highest priority group to the next highest priority group goes in a clockwise direction
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S configuration
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after assigning relative priorities to the four groups bonded to an asymmetric center, if the lowest-priority group is on a vertical axis in a fischer projection (or pointing away from the viewer in a perspective formula), an arrow drawn from the highest priority group to the next highest priority group goes in a counterclockwise direction
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plane-polarized light
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light that oscillates in a single plane passing through the direction the light travels
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polarized light
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light that oscillates in only one plane
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optically active
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rotates the plane of polarization of plane-polarized light
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optically inactive
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does not rotate the plane of polarization of plane-polarized light
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dextrorotatory |
the enantiomer that rotates the plane of polarization of plane-polarized light in a clockwise direction (+)
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levorotatory
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the enantiomer that rotates the plane of polarization of plane-polarized light in a counterclockwise direction (-)
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polarimeter
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an instrument that measures the rotation of the plane of polarization of plane-polarized light
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observed rotation
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the amount of rotation observed in a polarimeter
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specific rotation
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the amount of rotation that will be observed for a compound with a concentration of 1.0g/mL in a sample tube 1.0 decimeter long
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racemix mixture (raemate)
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a mixture of equal amount of a pair of enantiomers
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enantiomerically pure
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only one enantiomer is present in the sample
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diastereomer |
stereoisomers that are not enantiomers
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meso compound
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a compound that possesses asymmetric centers and a plane of symmetry; it is achiral, because it has a plane of symmetry
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plane of symmetry
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an imaginary plane that bisects a molecule into pieces that are a pair of mirror images
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amine inversion
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results when a compound containing an sp3 hybridized nitrogen with a nonbonding pair of electrons rapidly inverts
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configuration
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three-dimensional structure of a chiral compound, designated by R or S
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configurational isomers
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stereoisomers that cannot interconvert unless a covalent bond is broken, cis trans isomers and isomers with asymmetric centers are examples
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stereoisomers |
isomers that differ in the way the atoms are arranged in space
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