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Organic Chemistry Lecture 7
Organic Chemistry (Centro Escolar University)
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Derivatives of Hydrocarbons
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When a hydrogen atom is removed from an alkane, an alkyl group represented by R is formed
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When the alkyl group is attached to another atom or groups of atoms, then derivatives of
hydrocarbons are formed
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A derivative is something that is based on another source
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Hydrocarbon derivatives are based on simple hydrocarbon compounds that contain only
hydrogens and carbons
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Hydrocarbon derivatives contain at least one element other than hydrogen or carbon, such as
oxygen, nitrogen, or one of the halogen atoms (elements in column 7A)
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Most of the time, the atoms present in a hydrocarbon derivative are attached as part of a
distinct group. These groups are known as functional groups because they affect how the
compound contains hydrogen atoms and carbon
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Alcohol contains one or more hydroxyl (OH) group(s) directly attached to a carbon atoms(s), of
an aliphatic system (CH3OH) while a phenol contains -OH group(s) directly attached to a carbon
atom(s) of an aromatic system (C6H5OH)
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The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R-O/Ar-O)
yields another class of compounds known as ‘ethers’
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CH3OCH3 (dimethyl ether)
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May also visualize ethers as compounds formed by substituting the hydrogen atom of
the hydroxyl group of an alcohol or phenol by an alkyl or aryl group
Compounds Containing a Carbon-Heteroatom Single Bond
Structural/Constitutional Isomerism
Isomers
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These are compounds with the same molecular formula but different structures
Structural isomer: constitutional isomers that vary in the bonding attachments of atoms. Because of this
difference, structural isomers tend to differ in physical and/or chemical properties
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Chain isomers
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Also called skeletal isomers
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Isomers that differ in the arrangement of the carbon chain
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Have similar chemical properties but different physical properties
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Ex: pentanes
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Positional isomers
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Isomers that differ in the location of noncarbon or a double bond or triple bond
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Similar chemical properties but different physical properties
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There is a functional group, same number of carbon, same functional group, but located
in different carbon
Functional Isomers
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Isomers with structural differences that place them in different classes of organic
compounds
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Have very different chemical and physical properties
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Same number of carbon, but different functional group
Geometric and Optical Stereoisomerism
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Stereoisomers
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Isomers that have the same composition (that is, the same parts) but that differ in the
orientation of those parts in space
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Isomers with the same bonding attachments of atoms but different spatial orientations
Geometric isomer
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also called cis and trans isomers
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Stereoisomers in which atoms or groups of atoms display orientation differences around
a double bond or ring
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Same alignment but opposite
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Cis isomer:
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isomer where the same groups are on the same side of the C=C double bond
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Have similar (but not identical) chemical properties but different physical
properties
Trans isomer:
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isomer where the same groups are on the opposite side of the C=C double bond
When none or most of the groups attached to the double bond are not the same then geometric
isomers are notified or named with E or Z
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For the notification of this type of isomers the highest priority atom (highest atomic
number) attached to each double-bonded C is considered
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If two highest priority atoms stay on the same side of the isomer that is designated as Z
and if they are on the opposite side they are designated E
Optical isomer
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Also called enantiomers
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Enantiomers, are isomers that are identical in structure except where they differ as
mirror images that are not superimposable
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Nonsuperimposable mirror images contain a chirality center, that is, a carbon bonded to
four different substituents
(-) lactic acid
(+) lactic acid
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Enantiomers have identical physical constants, such as melting points, boiling points, density,
refractive index, viscosity, etc., but are said to be optically active since they can be distinguished
from each other by their ability to rotate the plane of polarized light in opposite directions
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A mixture of enantiomers in equal proportions is optically inactive and is called a racemic
mixture
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Enantiomers that rotate the plane of polarized light to the right are called dextrorotatory
(prefixed with +) and the ones which rotate to the left are called levorotatory (prefixed with -)
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