Organic Chemistry Nomenclature and Isomers

Question 1

___, the set of accepted conventions for naming compounds, is crucial to a discussion about organic chemistry

Answer 1

nomenclature

Question 2

The names of the four simplest \_\_\_ are 
CH4 Methane
CH3CH3 Ethane
CH3CH2CH3 Propane
CH3CH2CH2CH3 Butane

C5H12 Pentane
C6H14 Hexane
C7H16 Heptane
C8H18 Octane
C9H20 Nonane
C10H22 Decane
C11H24 Undecane
C12H26 Dodecane

Answer 2

alkanes

Question 3

1. Find the longest chain in the compound
   The longest continuous carbon ___ within the compound is taken as the backbone. If two or more chains are of equal length the most highly substituted chain (the one with the greatest number of other groups attached) takes precedence.

Answer 3

chain

Question 4

2. Number the chain
   Number the chain from one end in such a way that the lowest set of numbers is obtained for the ___ (which in alkanes are carbon groups not part of the main carbon chain)

Answer 4

substituents

Question 5

___ are named according to their appropriate prefix with the ending -yl.
CH3 Methyl
CH3CH2 Ethyl
CH3CH2CH2 Propyl
The prefix n- in the above example indicates an unbranched (“normal”) compound.

Answer 5

substituents

Question 6

If two or more groups are ___, the prefixes di-, tri-, tetra-, etc. are used

Answer 6

present

Question 7

Each substituent is assigned a number to identify its point of attachment to the ___ chain. If prefixes di-, tri-, tetra-, et., are used, a number is still necessary for each individual group

Answer 7

principal

Question 8

List the substituents in alphabetical order with their corresponding numbers. Prefixes such as di-, tri-, etc., as well as the hyphenated ___ (tert- [or t-], sec-, n-), are ignored in alphabetizing. In contrast, cyclo, iso, and neo are considered a part of the group name and are alphabetized Commas should be placed between numbers, and hyphens should be placed between numbers and words. You may also need to indicate the isomer you are describing - e.g., cis or trans, R or S, etc.

Answer 8

prefixes

Question 9

For ___, the substituents are named, and the carbon atoms are numbered around the ring starting from the point of greatest substitution

Answer 9

cycloalkanes

Question 10

Alkenes (or ___) are compounds containing carbon-carbon double bonds, The nomenclature rules are essentially the same as for alkanes except that the ending -ene is used rather than -ane

Answer 10

olefins

Question 11

Number the backbone so the double bond receives the lowest number possible. Remember that multiple ___ must be named using the prefixes di, tri, etc. and that each must receive a number. Substituents are named as they are for alkanes, and their positions are specified by the number of the backbone carbon atom to which they are attached. Frequently, an alkene group must be named as a substituent. In these cases, the systematic names may be used but common names are more popular.

Answer 11

double bonds

Question 12

Vinyl- derivatives are monosubstituted ___ (ethenyl-), and allyl- derivatives are propylenes substituted at the C-3 position (2-propenyl-). Methylene refers to the -CH2 group.

Answer 12

ethylene

Question 13

___ are named like cycloalkanes but with the suffix -ene rather than -ane. If the molecule has only a double bond and no other substituents, a number is not necessary

Answer 13

cycloalkenes

Question 14

Alkynes are ___ that possess carbon-carbon triple bonds. The suffix -yne replaces -ane in the parent alkane. The common name for ethyne is acetylene, and this name is used almost exclusively

Answer 14

compounds

Question 15

Compounds containing a halogen substituent are named following similar rules as those above while including the ___ as a substituent. If the halogen is the highest priority substituent, ensure it has the lower number when deciding from which end of the carbon chain to start counting. Alternatively, the haloalkane may be named as an alkyl halide. In this system, chloroethane is called ethyl chloride

Answer 15

halogen

Question 16

In the IUPAC system, alcohols are named by replacing the -e of the corresponding ___ with -ol. The chain is numbered such that the carbon attached to the hydroxyl group (-OH) receives the lowest number possible

Answer 16

alkane

Question 17

In compounds that possess a multiple ___ and hydroxyl group, numerical priority is given to the carbon attached to the -OH

Answer 17

bond

Question 18

A common system of ___ exists for alcohols in which the name of the alkyl group is combined with the word alcohol. These common names are used for simple alcohols.

Answer 18

nomenclature

Question 19

Molecules with two hysroxyl groups are called diols (or glycols) and are named with the suffix -diol. Two numbers are necessary to locate the two functional groups. Diols with hydroxyl groups on adjcent carbons are referred to as vicinal, and diols with hydroxyl groups on the same carbon are geminal. These terms apply for any two functional groups. ___ (also called carbonyl hydrates) are not commonly observed because they spontaneously lose water (dehydrate to produce carbonyl compounds.

Answer 19

geminal diols

Question 20

In the IUPAC system, ___ are named as derivatives of alkanes, and the larger alkyl group is chosen as the backbone. The their functionality is specified as an alkoxy- prefix, indicating the presence of an ether (oxy-), and the corresponding smaller alkyl group (alk-). The chain is numbered to give the ether the lowest position. Common names of ethers are derived by naming the two alkyl groups in alphabetical order and adding the word ether. The generic term “ether” refers to diethyl ether, a commonly used solvent

Answer 20

ethers

Question 21

For ___, numbering of the ring begins at the oxygen and proceeds to provide the lowest numbers for the substituents. Three-membered rings are termed oxiranes by IUPAC. The simplest of these are commonly called epoxides.

Answer 21

cyclic ethers

Question 22

___ are named according to the longest chain containing the aldehyde functional group. The suffix -al replaces the -e of the corresponding alkane. The carbonyl carbon receives the lowest number, although numbers are not always necessary since by definition an aldehyde is terminal and receives the number (1),

Answer 22

aldehydes

Question 23

The common names formaldehyde, acetaldehyde, and propionaldehyde are used almost exclusively instead of the IUPAC names ___ , ethanal, and propanal

Answer 23

methanal

Question 24

___ are named analogously with aldehydes but with -one as a suffix. If highest priority, the carbonyl group must be assigned the lowest possible number. In complex molecules, the carbonyl group can be named as a prefix with the term oxo-. Alternatively, the individual alkyl groups may be listed in alphabetical order and followed by the word ketone.

Answer 24

ketones

Question 25

A commonly used alternative to the numerical designation of ___ is to term the carbon atom adjacent to the carbonyl carbon as alpha and the carbon atoms successively along the chain as beta, gamma, and delta etc. This system is encountered with dicarbonyl compounds and halocarbonyl compounds

Answer 25

substituents

Question 26

___ are named with the ending -oic acid replacing the -e ending of the corresponding alkane. Carboxylic acids are terminal functional groups and, like aldehydes, are numbered (1)

Answer 26

carboxylic acids

Question 27

The ___ formic acid (methanoic acid), acetic acid (ethanoic acid), and propionic acid (propanoic acid) are used almost exclusively

Answer 27

common names

Question 28

The longest chain attached to the nitrogen atom is taken as the ___. For simple compounds, name the alkane and replace the final -e with -amine. More complex molecules are often named using the prefix amino-. The prefix N- is used to specify the location of an additional alkyl group attached to the nitrogen

Answer 28

backbone

Question 29

\_\_\_
amido-
-amide
Nitrile
cyano-
-nitrile
Aldehyde
oxo-
-al
Ketone
oxo-
-one
Thiol
sulfhydryl-
-thiol
Imine
imino-
-imine
Ether
alkoxy-
-ether
Sulfide
alkylthio-
Halide
halo-
Nitro
nitro-
Azide
azido-
Diazo
diazo-

Answer 29

amide

Question 30

Isomers are chemical ___ that have the same molecular formula but differ in structure, that is, in their atomic connectivity or the spatial orientation of their atoms. Isomers may be similar, sharing most or all of their physical and chemical properties, or thy may be very different

Answer 30

compounds

Question 31

Diastereomers and ___, enantiomers, and conformational isomers are stereoisomers

Answer 31

geometric isomers

Question 32

___, also known as constitutional isomers, are compounds that share only a molecular formula. Structural isomers differ in where and how atoms are connected to each other and thus often have very different chemical physical properties (such as melting point, boiling point, and solubility)

Answer 32

structural isomers

Question 33

___ are compounds that have the same connectivity between their atoms and differ from each other only in the way that their atoms are oriented in space. Cis-trans isomers, enantiomers, diastereomers, meso compounds, and conformational isomers are all types of stereoisomers

Answer 33

stereoisomers

Question 34

Cis-trans isomers, formerly known as geometric isomers, are compounds that differ in the position of substituents attached to the two carbons that form a double bond. Because a ___ cannot rotate, the substituents are fixed relative to one another and to the bond. If the substituents on the carbons are both above the double bond, they are on the same side, and the double bond is called cis. If one is above and one below, they are on opposite sides, and it is called trans double bond

Answer 34

double bond

Question 35

For ___ with more than one substituent on either carbon of the double bond, an alternative method of naming applies. The highest priority substituent attached to each double bonded carbon has to be determined. The following prioritization is the Cahn-Ingold-Prelog system, which is also used in R/S configurations for chiral centers. There are three rules for determining priority under this system
1. From the carbon of interest, determine the atomic weight of the first atom encountered along each bond. The group with the highest atomic weight atom has the highest priority.
2 If two atoms are the same, look at the next atom attached to each; the group that has the second atom with higher molecular weight is higher priority.
3. If two atoms are the same, a double bond takes priority over a single bond. This is a tie-breaker only; higher atomic weigh will always take priority over a double bond

Answer 35

compounds

Question 36

The alkene is called (Z) (from German zusammen, meaning together) if the two highest priority ___ on each carbon are both above or both below the double bond, or (E) (from German entgegen, meaning opposite) if they are on opposite sides

Answer 36

substituents

Question 37

Z = "Z"ame side
E = "E"pposite \_\_\_

Answer 37

side

Question 38

A ___ that is not super imposable upon its mirror image is called chiral. Achiral molecules are mirror images that can be superimposed; for example, the letter A is identical to its mirror image and there is achiral

Answer 38

molecule

Question 39

Carbon atoms are chiral only if they have four different substituents. Such a carbon atom is called asymmetric because it lacks a ___ or point of symmetry

Answer 39

asymmetric

Question 40

Pairs of ___ molecules that are nonsuperimposable mirror images are called enantiomers and are a specific type of stereoisomer discussed later in this chapter

Answer 40

chiral

Question 41

A carbon atom with only three different ___ such as 1,1-dibromoethane, has a plane of symmetry and is therefore achiral

Answer 41

substituents

Question 42

A three-dimensional molecule can be conveniently represented in two ___ in a Fischer projection

Answer 42

dimension

Question 43

In this system, horizontal ___ indicate bonds that project out from the plane of the page while vertical lines indicate bonds behind the plane of the page. The point of intersection of the lines represents a carbon atom. The Fischer projection of a molecule can be manipulated by interchanging any two pairs of substituents or by rotating the projection in the plane of the page by 180 degrees, and it will keep the same absolute configuration. If only one pair of substituents is interchanged or if the molecule is rotated by 90 degrees, the mirror image and thus the opposite enantiomer of the original compound is obtained

Answer 43

lines

Question 44

Fischer projections allow ___ of the configuration at a chiral center

Answer 44

straightforward determination

Question 45

A ___ describes the spatial arrangement of the atoms or functional groups of a stereoisomer

Answer 45

configuration

Question 46

The ___ of a chiral molecule is its configuration in relation to another chiral molecule. The absolute configuration of a chiral molecule describes the spatial arrangement of these atoms or groups within the molecule relative to each other. Absolute configuration is determined using the R/S naming convention, and relative configuration is compared between the R and S enantiomers

Answer 46

absolute configuration

Question 47

Step 1: Assign ___ to the four substituents using the same rules (the Cahn-Ingold -Prelog priority rules) as for E/Z isomers:

1. From the carbon of interest, determine the atomic weight of the first atom encountered along each bond. The group with the highest atomic weight atom has the highest priority
2. If two atoms are the same, look at the next atom attached to each; the group that has the second atom with higher molecular weight is higher priority
3. If two atoms are the same, a double bond takes priority over a single bond. This is a tie-breaker only; higher atomic weight will always take priority over a double bond

Answer 47

priority

Question 48

Step 2:
Proceeding from highest priority (1st) to second lowest (3rd), determine the order of ___ around the wheel as either clockwise or counterclockwise by drawing a loop that connects 1st and 2nd to 3rd priority, ignoring the 4th group. If the order is clockwise, the chiral center temporarily is called R (from Latin rectus, meaning right). If it is counterclockwise, it is temporarily called S (from Latin sinister, meaning left)

Answer 48

substituents

Question 49

Finally, look at the lowest (4th) priority group. If the group 4 is on the vertical line in a ___ projection or otherwise is going into the page, the molecule is oriented correctly, and the designation remains the same. If group4 is on the horizontal line or otherwise coming out of the page, the molecule is in the opposite orientation that it should be, so the temporary designation is swapped to the opposite designation (i.e., if the designation obtained in Step 2 was R but the 4th priority group is coming out of the page, the actual absolute configuration is S).
To provide a full name for a stereoisomer with a chiral center, the terms R and S are put in parentheses and separated from the rest of the name by a dash. If more than one asymmetric carbon is present, the location is specified by a number preceding the R or S within the parentheses and without a dash. Note that in the traditional approach to determining chirality, the molecule initially must be rotated to place the lowest priority group pointing toward the back. However, this can be problematic as it is easy to lose track of the relative positions of the substituents during this step. As the lower priority group is coming out of the page, it will appear the opposite of its true configuration, which avoids the difficult work of mentally rearranging the molecule

Answer 49

fischer

Question 50

Pairs of ___ (with opposite R and S designations) have identical chemical and physical properties with one exception: optical activity

Answer 50

enantiomers

Question 51

A compound is ___ active if it has the ability to rotate plane-polarized light

Answer 51

optically

Question 52

Ordinary ___ is unpolarized

Answer 52

light

Question 53

___ consists of waves vibrating all possible planes perpendicular to its direction of motion. A polarizing filter allows light waves oscillating only in a particular direction to pass, producing plane-polarized light

Answer 53

ordinary light

Question 54

If plane-polarized light is passed through a solution of an optically active ___, the molecule rotates the orientation of the polarized light by an angle alpha. The enantiomer of this compound will rotate light by the same amount, but in the opposite direction. A compound that rotates the plane-polarized light to the right, or clockwise (from the point of view of an observer seeing the light approach), is dextrorotary and is indicated by (+). A compound that rotates light toward the left, or counterclockwise, is levorotatory and is labeled (-). The direction of rotation cannot be determined from the structure of a molecule and is not related to its R or S designation. Instead, it must be determined experimentally.

Answer 54

compound

Question 55

The amount of ___ depends on the number of molecules that a light wave encounters, This depends on two factors: the concentration of the optically active compound and the length of the tube through which the light passes. Chemists have set standard conditions of 1 g/mL for concentration and 1 dm for length in order to compare the optical activities of different compounds. Rotations are measured at different concentrations and tube lengths can be converted to a standardized specific rotation (alpha) using the following equation:
specific rotation = observed rotation (alpha)/(concentration (g/ml) x length (dm))

Answer 55

rotation

Question 56

___ refers to the value obtained in an experiment with varying concentration or tube lengths. Specific rotation accounts for these various laboratory conditions and therefore can be used to compare the rotation of polarized light between different compounds. A racemic mixture, or racemate, is a mixture of equal concentrations of both the (+) and (-) enantiomers. The rotations cancel each other, and no optical activity is observed

Answer 56

observed rotation

Question 57

For any ___ with n chiral centers, there are 2^n possible stereoisomers.

Answer 57

molecule

Question 58

Diastereomers are ___ that are not mirror images

Answer 58

stereoisomers

Question 59

Diastereomers that differ at only one carbon make up special pairs called ___, which are particularly important in the chemistry of carbohydrates

Answer 59

epimers

Question 60

Meso compounds are molecules with chiral centers that also have an internal ___ of symmetry

Answer 60

plane

Question 61

One half of the ___ has an S enantiomer, and the other half has its matching R enantiomer. If such a plane of symmetry exists, the molecule is not optically active, because the rotation of light by one chiral center is matched by the opposite rotation by the other chiral center

Answer 61

molecule

Question 62

___ are compounds that differ only by rotation about one or more single bonds

Answer 62

conformational isomers

Question 63

___ conformations can be seen when the molecule is depicted in a Newman projection, in which the line of sight extends along a carbon-carbon bond axis. Because the view of the second carbon atom is blocked by the first, the second carbon is depicted as a large circle at the back and the first carbon is depicted as the intersection of its three other bonds in front. The different conformations are encountered as the molecule is rotated about the axis between the two carbons. The classic example for demonstrating conformational isomerism in a straight chain molecule is n-butane. In a Newman projection, the line of sight extends through the C-2-C-3 bond axis

Answer 63

conformational isomer

Question 64

The most ___ n-butane is found when the two methyl groups (C-1 and C-4) are oriented 180 degrees from each other. There is no overlap of atoms along the line of sight (besides C-2 and C-3), so the molecule is said to be in a staggered conformation. Specifically, it is called the anti conformation, because the two methyl groups are antiperiplanar to each other. This particular orientation is very stable and thus represents an energy minimum because all atoms are far apart, minimizing repulsive steric interactions

Answer 64

stable conformation

Question 65

The other type of staggered ___, called gauche, occurs when the two methyl groups are sixty degrees apart. In order to convert from the anti to the gauche conformation, the molecule must pass through an eclipsed conformation, in which the two methyl groups are 120 degrees apart and overlap with the H atoms on the adjacent carbon. When the two methyl groups overlap with each other, the molecule is said to be totally eclipsed and is in its highest energy state

Answer 65

conformation

Question 66

If the ___ do not possess sufficient energy to cross the energy barrier, they may not rotate at all

Answer 66

molecules

Question 67

In cycloalkanes, ___ arises from three factors: angle strain, torsional strain, and nonbonded strain

Answer 67

ring strain

Question 68

___ results when bond angles deviate from their ideal value (109.5 degrees for sp3 hybridized carbons); torsional strain results when cyclic molecule must assume conformations that have eclipsed interactions; and nonbonded strain (van der Waals repulsion) results when atoms or groups compete for the same space. In order to alleviate these three types of strain, cycloalkanes attempt to adopt nonplanar conformations. Cyclobutane puckers into a slight V shape, cyclopentane adopts what is called the envelope conformation, and cyclohexane exists mainly in three conformations called the chair, the boat, and the twist or skew-boat

Answer 68

angle strain

Question 69

The most stable conformation of cyclohexane is the ___ conformation. In this conformation, all three types of strain are eliminated. The hydrogen atoms that are perpendicular to the plane of the ring are called axial, and those parallel to the plane of the ring are called equatorial. The axial-equatorial orientations alternate around the ring.
The chair conformation has two forms that can be thought of as “left facing’ and “right facing.” The boat conformation is adopted when the chair “flips” and converts to the other chair conformation. When this happens, hydrogen atoms that were equatorial become axial, and vice versa, in the new chair. In the boat conformation, all of the atoms are eclipsed, creating a high-energy state. To avoid this strain, the boat can twist into a slightly more stable form called the twist or skew-boat conformation. In the chair form, the atoms are in the staggered gauche conformation, thus contributing to the greater stability compared to the boat form

Answer 69

chair

Question 70

The interconversion between the two chairs can be slowed or even prevented if a sterically bulky group is attached to the ring. The equatorial position is favored over the axial position because of ___ with other axial substituents. Thus, a large group such as t-butyl can essentially lock the molecule in one conformation

Answer 70

steric repulsion

Question 71

Different isomers can exist for ___. If both substituents are located on the same side of the ring, the molecule is called cis; if the two groups are on opposite sides of the ring, it is called trans

Answer 71

disubstituted cycloalkanes

Question 72

Note that the chair form shows that ___ can be either above or below the plane of the ring, shown by the “slant” of the bond connecting them to their ring carbons

Answer 72

equatorial constituents