Naming Alkenes

11 Key excerpts on "Naming Alkenes"

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  eBook - ePub

  Understanding Advanced Organic and Analytical Chemistry

  The Learner's ApproachRevised Edition

  • Kim Seng Chan, Jeanne Tan;;;(Authors)
  • 2016(Publication Date)
  • WS EDUCATION

    (Publisher)

  CHAPTER 5

  Alkenes

  5.1 Introduction

  Alkenes are unsaturated hydrocarbons containing the C=C double bond. They have the general formula Cn H

  2n

  . Sharing this same general formula are the cycloalkanes, which are constitutional/structural isomers to the corresponding alkenes. Apart from functional group isomerism, constitutional/structural isomerism in alkenes can also arise due to the different degree of branching in the main carbon chain of their molecules (chain isomerism) and the location of the C=C bond (positional isomerism).

  Alkenes also exhibit cis-trans isomerism, otherwise known as geometrical isomerism (see Chapter 2 ). This form of stereoisomerism is attributed to the restricted rotation about the C=C bond.

  As the doubly bonded carbon atoms are sp2 hybridized, the geometry about each of them is trigonal planar. To show the trigonal planar geometry, the structure of an alkene is normally drawn in such a way as to depict an angle of 120° about the double bond, as follows:

  This form of drawing is especially important in illustrating both the cis and trans isomers.

  5.2 Nomenclature

  For alkenes, their chemical names end with the suffix −ene. Table 5.1 lists the names of the first few members of the alkene family. For an alkene with four carbon atoms onwards, there exists different ways in which the carbon atoms can be connected to each other, hence giving rise to the notion of constitutional/structural isomerism (see Chapter 2 ). For instance, both but-1-ene and but-2-ene have a chain of four carbon atoms. The difference between them is the location of the C=C bond.

  Table 5.1

  The word “butene” does not just wrongfully account for the two constitutional/structural isomers mentioned above, ambiguity is also found in the word “but-2-ene,”which actually constitutes a pair of cis-trans (geometrical) isomers:

  Hence, “butene” actually stands for a total of three distinct compounds – but-1-ene, cis-but-2-ene and trans

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  Brown's Introduction to Organic Chemistry

  • William H. Brown, Thomas Poon(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  A. IUPAC Names We form IUPAC names of alkenes by changing the ‐an‐ infix of the parent alkane to ‐en‐ (Section 3.5). Hence, CH 2 CH 2 is named ethene, and CH 3 CH CH 2 is named propene. In higher alkenes, where isomers exist that differ in the location of the double bond, we use a numbering system. We number the longest carbon chain that contains the double bond in the direction that gives the carbon atoms of the double bond the lower set of numbers. We then use the number of the first carbon of the double bond to show its location. We name branched or substituted alkenes in a manner similar to the way we name alkanes (Section 3.3). We number the carbon atoms, locate the double bond, locate and name substituent groups, and name the main (parent) chain. 1-Hexene 6 4 2 1 3 5 CH 3 CH 2 CH 2 CH 2 CH CH 2 1 2 3 4 5 6 2-Ethyl-3-methyl-1-pentene CH 3 CH 2 CHC CH 2 CH 3 CH 2 CH 3 1 2 3 4 5 5 3 1 2 4 4-Methyl-1-hexene 6 4 2 1 3 5 CH 3 CH 2 CHCH 2 CH CH 2 CH 3 1 2 3 4 5 6 in Naming Alkenes, the parent chain is the longest chain containing the entire C C bond, even if a different chain that doesn’t contain the C C bond is longer Note that there is a six‐carbon chain in 2‐ethyl‐3‐methyl‐1‐pentene. However, because the longest chain that contains the carbon–carbon double bond has only five carbons, the par- ent hydrocarbon is pentane, and we name the molecule as a disubstituted 1‐pentene. 4.2 108 C H A P T E R 4 Alkenes and Alkynes We form IUPAC names of alkynes by changing the ‐an‐ infix of the parent alkane to ‐yn‐ (Section 3.5). Thus, HC CH is named ethyne, and CH 3 C CH is named propyne. The IUPAC system retains the name acetylene; therefore, there are two acceptable names for HC CH: ethyne and acetylene. Of these two names, acetylene is used much more frequently. For larger molecules, we number the longest carbon chain that contains the triple bond from the end that gives the triply bonded carbons the lower set of numbers.

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  Klein's Organic Chemistry

  • David R. Klein(Author)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  The system of nam- ing chemical compounds, or nomenclature, will be developed and refined throughout the remaining chapters of this book. 4.2 NOMENCLATURE OF ALKANES An Introduction to IUPAC Nomenclature In the early nineteenth century, organic compounds were often named at the whim of their discover- ers. Here are just a few examples: Formic acid Isolated from ants and named after the Latin word for ant, formica H OH O Urea Isolated from urine H 2 N NH 2 O Barbituric acid Adolf von Baeyer named this compound in honor of a woman named Barbara N N O O O H H Morphine A painkiller named after the Greek god of dreams, Morpheus O HO HO N H A large number of compounds were given names that became part of the common language shared by chemists. Many of these common names are still in use today. As the number of known compounds grew, a pressing need arose for a systematic method for naming compounds. In 1892, a group of 34 European chemists met in Switzerland and developed a system of organic nomenclature called the Geneva rules. The group ultimately became known as the International Union of Pure and Applied Chemistry, or IUPAC (pronounced “I–YOU–PACK”). The original Geneva rules have been regularly revised and updated and are now called IUPAC nomenclature. DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter. • Molecular Orbital Theory (Section 1.8) • Predicting Geometry (Section 1.10) • Bond-Line Structures (Section 2.2) • Three-Dimensional Bond-Line Structures (Section 2.6) 134 CHAPTER 4 Alkanes and Cycloalkanes Names produced by IUPAC rules are called systematic names. There are many rules, and we cannot possibly study all of them. The upcoming sections are meant to serve as an introduction to IUPAC nomenclature.

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  Organic Chemistry

  • David R. Klein(Author)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Our discussion of conformational analysis will involve the comparison of many different compounds and will be more efficient if we can refer to compounds by name. A system of rules for naming alkanes and cycloalkanes will be developed prior to our discussion of molecular flexibility. 4.1 Introduction to Alkanes 4.2 Nomenclature of Alkanes 4.3 Constitutional Isomers of Alkanes 4.4 Relative Stability of Isomeric Alkanes 4.5 Sources and Uses of Alkanes 4.6 Drawing Newman Projections 4.7 Conformational Analysis of Ethane and Propane 4.8 Conformational Analysis of Butane 4.9 Cycloalkanes 4.10 Conformations of Cyclohexane 4.11 Drawing Chair Conformations 4.12 Monosubstituted Cyclohexane 4.13 Disubstituted Cyclohexane 4.14 cis-trans Stereoisomerism 4.15 Polycyclic Systems 4 4.2 Nomenclature of Alkanes 133 4.1 Introduction to Alkanes Recall that hydrocarbons are compounds comprised of only C and H; for example: C C H H H H H H Ethane C 2 H 6 C C H H H H Ethylene C 2 H 4 C C H H Acetylene C 2 H 2 Benzene C 6 H 6 Ethane is unlike the other examples in that it has no π bonds. Hydrocarbons that lack π bonds are called saturated hydrocarbons, or alkanes. The names of these compounds usually end with the suffix “-ane,” as seen in the following examples: Propane Butane Pentane This chapter will focus on alkanes, beginning with a procedure for naming them. The system of nam- ing chemical compounds, or nomenclature, will be developed and refined throughout the remaining chapters of this book. 4.2 Nomenclature of Alkanes An Introduction to IUPAC Nomenclature In the early nineteenth century, organic compounds were often named at the whim of their discover- ers.

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  Organic Chemistry

  An Acid-Base Approach, Third Edition

  • Michael B. Smith(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  There are a vast number of alkanes, and each unique structure requires a unique name. The nomenclature system used is based on the number of carbon atoms in the longest continuous chain. Branches are identified by the number of carbon atoms and their position on the longest chain. To accommodate the myriad variations in structure, a set of “rules” have been devised that are universally used to name organic molecules. The organization that supervises these rules is the International Union of Pure and Applied Chemistry, I.U.P.A.C. or just IUPAC.

  4.3.1 Prefixes and Simple Alkanes

  The IUPAC nomenclature rules2 allow any organic molecule to be named. Once the longest continuous chain is identified, a prefix indicates the number of carbon atoms, and a suffix describes the class of molecules . The unique suffix used for alkanes is -ane . The prefix for the number of carbons is based on the first 20 straight-chain alkanes, C1 to C20 , listed in Table 4.1 . 2 A one-carbon unit has the prefix meth- ; two carbons are eth- ; three carbons are prop- ; four carbons are but- ; five, six seven, eight, nine, and ten are derived from the Latin terms: pent- , hex- ; hept- , oct- , non- , dec- . To identify C 11-C 20 linear alkanes the prefixes use the eq uivalent of 1+10, 2+10, 3+10, and so on. The prefixes are undec- (11), dodec- (12), tridec- (13), tetradec- (14), pentadec- (15), hexadec- (16), heptadec- (17), octadec- (18), nonadec- (19), and icos- (20). The structures and names of the first twenty alkanes are shown in Table 4.1 . The structures are drawn as a condensed formula CH3 (CH2 )n CH3 .

  2 Flectcher, J.H.; Dermer, O.C.; Fox, R.B. Nomenclature of Organic Compounds. Principles and Practice, 1974, American Chemical Society, Washington, D.C., pp. 6–11.

  Table 4.1 Nomenclature For Alkanes With Linear Chains Of Carbon Atoms

  When the longest linear (unbranched) chain has an atom or group of atoms attached, that atom or group is called a substituent . If the substituent has only sp3 hybridized carbon atoms, each with attached hydrogen atoms, it is called an alkyl group , or an alkyl substituent . For a hydrocarbon substituent, the same prefix used in Table 4.1 indicates the number of carbon atoms, meth→icos but the suffix for the alkyl substituent is -yl

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  Solomons' Organic Chemistry

  • T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  4.5 HOW TO NAME ALKENES AND CYCLOALKENES 159 4. Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the 1 and 2 positions and that also gives the substituent groups the lower numbers at the first point of difference. With substituted cycloalkenes it is not neces- sary to specify the position of the double bond since it will always begin with C1 and C2. The two examples shown here illustrate the application of these rules: 3,5-Dimethylcyclohexene (not 4,6-dimethylcyclohexene) 1-Methylcyclopentene (not 2-methylcyclopentene) 3 2 4 5 3 2 5 6 4 1 1 5. Name compounds containing a double bond and an alcohol group as alkenols (or cycloalkenols) and give the alcohol carbon the lower number: OH 3 2 1 OH 2 4 5 3 1 4-Methyl-3-penten-2-ol or 4-methylpent-3-en-2-ol 2-Methyl-2-cyclohexen-1-ol or 2-methylcyclohex-2-en-1-ol 6. Two frequently encountered alkenyl groups are the vinyl group and the allyl group: The allyl group The vinyl group Using substitutive nomenclature, the vinyl and allyl groups are called ethenyl and prop-2-en-1-yl, respectively. The following examples illustrate how these names are employed: Cl 3-Chloropropene or allyl chloride (common) Br Bromoethene or vinyl bromide (common) Ethenylcyclopropane or vinylcyclopropane OH 3-(Prop-2-en-1-yl)cyclohexan-1-ol or 3-allylcyclohexanol 7. If two identical or substantial groups are on the same side of the double bond, the compound can be designated cis; if they are on opposite sides it can be designated trans: Cl Cl Cl Cl trans-1,2-Dichloroethene cis-1,2-Dichloroethene (In Section 7.2 we shall see another method for designating the geometry of the double bond.) 160 CHAPTER 4 NOMENCLATURE AND CONFORMATIONS OF ALKANES AND CYCLOALKANES 4.6 HOW TO NAME ALKYNES Alkynes are named in much the same way as alkenes. Unbranched alkynes, for example, are named by replacing the -ane of the name of the corresponding alkane with the ending -yne.

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  Organic Chemistry

  • T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  For these reasons, we begin our study of the IUPAC system with the rules for naming alkanes and then study the rules for alkyl halides and alcohols. The ending for all of the names of alkanes is -ane. The stems of the names of most of the alkanes (above C 4 ) are of Greek and Latin origin. Learning the stems is like learning to count in organic chemistry. Thus, one, two, three, four, and five become meth-, eth-, prop-, but-, and pent-. The names for some unbranched alkanes are listed in Table 4.2. *The complete IUPAC rules for nomenclature can be found through links at the IUPAC website. TABLE 4.2 The Unbranched Alkanes Name Number of Carbon Atoms Structure Name Number of Carbon Atoms Structure Methane 1 CH 4 Undecane 11 CH 3 (CH 2 ) 9 CH 3 Ethane 2 CH 3 CH 3 Dodecane 12 CH 3 (CH 2 ) 10 CH 3 Propane 3 CH 3 CH 2 CH 3 Tridecane 13 CH 3 (CH 2 ) 11 CH 3 Butane 4 CH 3 (CH 2 ) 2 CH 3 Tetradecane 14 CH 3 (CH 2 ) 12 CH 3 Pentane 5 CH 3 (CH 2 ) 3 CH 3 Pentadecane 15 CH 3 (CH 2 ) 13 CH 3 Hexane 6 CH 3 (CH 2 ) 4 CH 3 Hexadecane 16 CH 3 (CH 2 ) 14 CH 3 Heptane 7 CH 3 (CH 2 ) 5 CH 3 Heptadecane 17 CH 3 (CH 2 ) 15 CH 3 Octane 8 CH 3 (CH 2 ) 6 CH 3 Octadecane 18 CH 3 (CH 2 ) 16 CH 3 Nonane 9 CH 3 (CH 2 ) 7 CH 3 Nonadecane 19 CH 3 (CH 2 ) 17 CH 3 Decane 10 CH 3 (CH 2 ) 8 CH 3 Eicosane 20 CH 3 (CH 2 ) 18 CH 3 a Unless otherwise indicated, all boiling points given in this book are at 1 atm or 760 torr. b The index of refraction is a measure of the ability of the alkane to bend (refract) light rays. The values reported are for light of the D line of the sodium spectrum (n D ). 4.3 How To Name Alkanes, Alkyl Halides, and Alcohols: the IUPAC System 153 4.3A How To Name Unbranched Alkyl Groups If we remove one hydrogen atom from an alkane, we obtain what is called an alkyl group.

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  eBook - PDF

  Organic Chemistry

  • T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Designate the loca- tion of the double bond by using the number of the first atom of the double bond as a prefix. The locant for the alkene suffix may precede the parent name or be placed immediately before the suffix. We will show examples of both styles: 2-Hexene (not 4-hexene) CH 3 CH==CHCH 2 CH 2 CH 3 1-Butene (not 3-butene) 1 2 3 4 CH 2 ==CHCH 2 CH 3 3. Indicate the locations of the substituent groups by the numbers of the carbon atoms to which they are attached: 4 3 2 1 6 4 5 3 2 1 2,5-Dimethyl-2-hexene or 2,5-dimethylhex-2-ene 5 3 6 4 1 2 CH 3 CH 3 CH==CHCH 2 C —CH 3 CH 3 1 2 4 3 CH 3 CH==CHCH 2 Cl 1-Chloro-2-butene or 1-chlorobut-2-ene 5,5-Dimethyl-2-hexene or 5,5-dimethylhex-2-ene 2-Methyl-2-butene or 2-methylbut-2-ene Many older names for alkenes are still in common use. Ethene is often called ethylene, propene is often called propylene, and 2-methylpropene is often called isobutylene. 2-Methylpropene Isobutylene Propene Propylene Ethene Ethylene IUPAC: Common: 4.5 HOW TO NAME ALKENES AND CYCLOALKENES 159 4. Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the 1 and 2 positions and that also gives the substituent groups the lower numbers at the first point of difference. With substituted cycloalkenes it is not neces- sary to specify the position of the double bond since it will always begin with C1 and C2. The two examples shown here illustrate the application of these rules: 3,5-Dimethylcyclohexene (not 4,6-dimethylcyclohexene) 1-Methylcyclopentene (not 2-methylcyclopentene) 3 2 4 5 3 2 5 6 4 1 1 5. Name compounds containing a double bond and an alcohol group as alkenols (or cycloalkenols) and give the alcohol carbon the lower number: OH 3 2 1 OH 2 4 5 3 1 4-Methyl-3-penten-2-ol or 4-methylpent-3-en-2-ol 2-Methyl-2-cyclohexen-1-ol or 2-methylcyclohex-2-en-1-ol 6.

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  Organic Chemistry

  Fundamentals and Concepts

  • John M. McIntosh(Author)
  • 2022(Publication Date)
  • De Gruyter

    (Publisher)

  C can be written 2-pentene or pent-2-ene. Either is acceptable.

  Compounds that have more than one double bond are dienes (

  2 ⁢ C

  = C

  ), trienes (

  3 ⁢ C

  = C

  ), etc. The naming and numbering systems are covered by the rule given above. The main chain must contain as many of the double bonds as possible and the numbering must give precedence to the functional groups. To make the names of these compounds easier to pronounce, the root word describing the chain length is combined with the word “diene” or “triene”, etc., using the letter “a” as a bridge. Thus, names like 1,3-octadiene or 1,3,5-hexatriene are formed.

  Q16-2. Provide IUPAC names for the following compounds

  If chains containing double bonds are substituents, the usual methods apply. Thus, the name of

  CH 2

  =

  CH -

  as a substituent is ethenyl. Propene (

  CH 2

  =

  CHCH 3

  ) can give rise to three possible substituents depending on where the hydrogen is removed from the chain. These are

  - CH

  =

  CHCH 3

  (1-propenyl),

  CH 2

  =

  CHCH 2

  -

  (2-propenyl), and

  CH 2

  =

  CCH 3

  (1-methyl-1-ethenyl). The point of attachment of the substituent chain to the main chain is always given the number 1. You should be able to see these derivations.

  Q16-3. Provide complete IUPAC names for the following compounds

  The Index of Hydrogen Deficiency II

  As was outlined in the previous chapter on alkanes, the ratio of carbon to hydrogen in any alkane is given by the expression

  C n

  ⁢

  H

  2 ⁢ n

  + 2

  . In order to create one double bond in a chain and maintain the valency of carbon at four, two hydrogens must be removed from adjacent carbons. This will then make the general formula

  C n

  ⁢

  H

  2 ⁢ n

  . This simple fact allows the calculation of the number of double bonds or their equivalents (the importance of this phrase will be seen shortly) in any molecule just from the molecular formula. Calculate the number of hydrogens that would be needed to create an alkane from the given number of carbon atoms. Subtract from this the number of hydrogens actually present. Divide this difference by two and the result is the number of double bonds or their equivalents present in the molecule. This is the Index of Hydrogen Deficiency (IHD). Some texts refer to this as SODAR (Sum Of Double bonds And R

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  Organic Chemistry

  A Mechanistic Approach

  • Penny Chaloner(Author)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  37 3.1 ALKENES 3.1.1 BONDING IN ALKENES The next group of hydrocarbons that we will study is the alkenes (old name olefins), compounds containing one or more carbon–carbon double bonds. The first member of the class is ethene ( 3.1) in which there is a double bond between the two carbon atoms. The old name for this com- pound was ethylene, and this is still widely used in the polymer industry. There are two carbon– carbon bonds along the same direction—so clearly, we cannot use sp 3 hybrid orbitals, which we used to make alkanes, for this molecule. 3.1 C C H H H H In order to describe a carbon–carbon double bond, we need to return to the electronic configura- tion of carbon: C 1s 2 2s 2 2p x 1 2p y 1 2p z 0 As before, we formally promote one electron to obtain C 1s 2 2s 1 2p x 1 2p y 1 2p z 1 This time, we set aside the 2p z orbital, which we will use to make a π-bond, and take the 2s, 2p x , and 2p y orbitals to make three 2p 2 hybrid orbitals. These sp 2 hybrids point toward the corners of an equilateral triangle (by VSEPR or some serious mathematics), with angles of 120 o between them. The calculated orbitals are shown in Figure 3.1. We can now use these orbitals with the 1s orbitals from hydrogen to make the σ-bonds of ethene (3.2). The σ-bonds to hydrogen are each made from a hydrogen 1s and the sp 2 orbital. The carbon–car- bon σ-bond is formed from two sp 2 orbitals, coming together effectively nose to nose. Since we used s, p x , and p y to make these hybrid orbitals, the σ-framework must be planar in the xy plane (Figure 3.2). 3.2, σ-framework of ethene C C H H H H Alkenes, Alkynes, and Aromatic Compounds 3 38 3.1 Alkenes On each carbon atom, we are left with a 2p z orbital containing one electron. The orbitals are brought together side to side (they are perpendicular to the plane of the rest of the molecule) and combined to give a π- and a π*-orbital (Figure 3.3). We have two electrons to accommodate, and these are both in the π-orbital.

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  eBook - PDF

  Introduction to General, Organic, and Biochemistry

  • Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
  • 2019(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Resonance hybrid A molecule best described as a hybrid of two or more Lewis contributing structures 12.7 Structure of Benzene | 369 Copyright 2020 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 12.8 Naming Aromatic Compounds A. One Substituent Monosubstituted alkylbenzenes are named as derivatives of benzene— for example, ethylbenzene. The IUPAC system retains certain common names for several of the simpler monosubstituted alkylbenzenes, including toluene and styrene. Ethylbenzene CH 2 CH 3 Toluene CH 3 Styrene CH CH 2 The IUPAC system also retains common names for the following compounds: Phenol OH Anisole OCH 3 Aniline NH 2 Benzaldehyde C 9 H O Benzoic acid C 9 OH O The substituent group derived by loss of an H from benzene is called a phenyl group , C 6 H 5 i , the common symbol for which is Ph i . In mole-cules containing other functional groups, phenyl groups are often named as substituents. Phenyl group (C 6 H 5 9 ; Ph 9 ) 1-Phenylcyclohexene 4-Phenyl-1-butene 4 3 1 2 B. Two Substituents When two substituents occur on a benzene ring, three isomers are possible. We locate the substituents either by numbering the atoms of the ring or by using the locators ortho (o), meta (m) , and para (p) . In IUPAC nomencla-ture, the numbers 1,2- are equivalent to ortho (Greek: straight); 1,3- to meta (Greek: after); and 1,4- to para (Greek: beyond).

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