Section outline

  • Representation of branched alkanes with colored blocks indicating molecular structure.

    Who is my great-aunt?
    ::我的大姨妈是谁?

    Tracing your family tree can be both fun and exciting. But, it helps to know the exact names of your family members in order to do this correctly. Just a first name or middle name or last name is not enough. A traceable family tree is one in which all relatives are carefully and precisely identified. After all, you would prefer that great-great-great-uncle to be royalty and not a horse thief.
    ::追寻您的家族树既有趣又令人兴奋。 但是,为了正确做到这一点,它有助于了解您家庭成员的确切姓名。 仅仅一个名字或中名或姓是不够的。 一个可追踪的家族树是所有亲戚都仔细和准确地识别的树。 毕竟,你更希望伟大的大叔成为皇室,而不是一个偷马贼。

    Branched Alkanes
    ::分管的阿尔卡内斯

    Beginning with butane, there is an alternate structure possible that is not a straight chain. The structural formulas below show a structure with a three-carbon chain that has a –CH 3 group attached to the middle carbon.
    ::从丁烷开始,可能有一种替代结构,它不是一条直线链。 下面的结构公式显示的是三碳链结构,其中中间碳有一个 — — CH3组。

     

    Structural formula of 2-methylpropane, a branched isomer of butane with four carbons.

    The name of this molecule is 2-methylpropane. The is still C 4 H 10 , which is the same formula as butane. A structural isomer is one of multiple molecules that have the same molecular formula, but different structural formulas. Butane and 2-methylpropane are structural isomers.
    ::该分子的名称是2-甲基丙烷。 仍然是C4H10, 与丁烷的公式相同。 结构异构体是多个分子的分子之一, 具有相同的分子公式, 但不同的结构公式。 丁烷和2-甲基丙烷是结构异构体。

    2-methylpropane is an example of a type of alkane called a branched alkane. The IUPAC system of nomenclature for branched alkanes follows a set of steps which will be applied to the example molecule below.
    ::2-甲基丙烷是被称为分支烷的一种烷的一个例子,国际化联的分支烷命名系统遵循一系列步骤,将适用于以下的示例分子。

     

    Structural formula of 5-ethyl-3-methyloctane with numbered carbon atoms and substituents.

    1. Find the longest continuous chain of carbon atoms in the molecule. This is called the parent chain. In the example, the longest chain is eight carbon atoms and so the parent is octane.
      ::查找分子中最长的碳原子连续链。 这称为母链。 例如, 最长的链是八个碳原子, 因此母体是辛烷 。
    2. Number the carbon atoms in the parent chain. To do this, start at the end that will give the smallest numbers possible to the carbon atoms where the branches originate. In the example above, the branches are on carbons 3 and 5 when the chain is numbered left-to-right. If it were to be numbered right-to-left, the branches would be on carbons 4 and 6, so the left-to-right order is preferable.
      ::母链中的碳原子数量。 要做到这一点, 开始在结尾处给树枝来源的碳原子尽可能最小的数量。 在以上例子中, 当链条被从左到右编号时, 树枝在碳3和碳5上。 如果将树枝编号为右对左, 树枝将会在碳4和碳6上, 因此左对右顺序比较可取 。
    3. The atoms attached to the parent chain are called substituents. A substituent that is a hydrocarbon is called an alkyl group . The names of alkyl groups use the same prefixes as the alkanes, but with a –yl suffix. So a 1-carbon alkyl group is a methyl group, a 2-carbon alkyl group is an ethyl group, and so on. The substituents are named by placing the number from the parent carbon chain in front of the name of the substituent. In the current example, we have 3-methyl and 5-ethyl substituents.
      ::附属于母链的原子被称为替代物。 碳氢化合物的替代物被称为烷基集团。 烷基集团的名称使用与alkanes相同的前缀,但有-yl 后缀。 因此, 1-碳烷基集团是一个甲基集团,2-碳烷基集团是一个乙基集团,等等。 替代物的名称是将母碳链的编号放在替代物名称前面。 在目前的例子中,我们有3-甲基和5乙基替代物。
    4. Use a prefix to indicate the appearance of more than one of the same substituent in the structural formula. Two of the same group is bi-, three is tri-, four is tetra-, etc. For example, if methyl groups were attached to both carbons 2 and 3, that part of the name would be 2, 3-dimethyl-. This rule does not apply to the current structure above.
      ::使用一个前缀来表示结构公式中同一替代方中不止一个的外观。 同一组中有两个为双组, 三个为三组, 四个为四组等。 例如, 如果甲基组同时附于碳2和3, 其部分名称为 2, 3- 二甲基-, 则该规则不适用于上述当前结构 。
    5. Multiple different substituents are listed in alphabetical order. Ignore any of the prefixes from rule 4. In the current example, the 5-ethyl- comes before the 3-methyl.
      ::多个不同的替代机构按字母顺序排列。 忽略第4条规则的任何前缀。 在目前的例子中, 5- 乙基- 出现在 3- 甲基之前 。
    6. Commas are used to separate multiple numbers. Hyphens come between the number and the name of a substituent. The parent name comes immediately after the last substituent. There are no blank spaces in the name.
      ::逗号用于分隔多个数字。连字符在数字和替代名称之间产生。父名在最后一个替代名称之后立即出现。在名称中没有空白。

    The correct name for the above structure according to the IUPAC system is 5-ethyl-3-methyloctane.
    ::根据国际化联系统,上述结构的正确名称为5-乙基-3-甲基辛烷。

     

     

     

    Review
    ::回顾

    1. What is an alkyl group?
      ::什么是烷基组?
    2. How are alkyl substituents listed?
      ::烷基替代物如何列入?
    3. If there are three methyl groups on the same carbon, what is the prefix used?
      ::如果在同一碳上有三个甲基组,使用什么前缀?