Reading A Chemical Graph
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Shorthand Notation:

  • The point where two lines meet or the end of a line (a vertex) represents a carbon with an implicit number of hydrogens.
  • The number of lines drawn to a vertex plus the implicit number of hydrogens add up to four.
  • The implicit number of hydrogens at a carbon is a complement of 4 of the number of lines draw to the vertex.
  • If you draw an atomic symbol at the vertex or draw hydrogens to the vertex then the number of hydrogens is no longer implicit, you must draw out the hydrogens that you intend to represent.
  • You must explicitly draw out the hydrogens to other atoms besides carbon.

Exam question 1:  How many carbons are in the given chemical structure?

Methane, Methyl, Methylene, and Methine:

  • A compound with one carbon and four hydrogens is a called methane, CH4, the major component of natural gas.
  • A carbon with three hydrogens is called a methyl, CH3.
    • The suffix yl is used to indicate that one group of atoms is attached to another thing.
  • A carbon with two hydrogens is called a methylene, CH2.
  • A carbon with one hydrogen is called a methine, CH.

Exam question 2:  How many methyls, methylenes or methines are in a given chemical structure?

Primary, Secondary, Tertiary and Quaternary Carbons and Nitrogens:

  • A carbon or a nitrogen with one bond to another carbon is referred to as being primary. 1.
  • A carbon or a nitrogen with bonds to two other carbons is referred to a being secondary, 2.
  • A carbon or a nitrogen with bonds to three other carbons is referred to as being tertiary, 3.
  • A carbon or a nitrogen with bonds to four other carbons is referred to as being quaternary, 4.
  • Oxygen compounds are referred to as being primary, secondary, and tertiary for other reasons.

Exam question 3:  How many primary, secondary, tertiary or quaternary carbons or nitrogens are in a given chemical structure?

Hydrogens versus Degree:

  • Not all methyls are primary, methylenes secondary, or methines tertiary.
  • The strong association of methyls as primary, methylens as secondary, and methines as tertiary only holds for saturated hydrocarbons.
  • Saturated compounds have no multiple bonds (lines) between atoms.
  • Hydrocarbons have only carbons and hydrogens, and are used mostly to burn as fuels.

Exam question 4:  How many primary methyls, methylenes or methines, secondary methylenes or methines, or tertiary methines are in a given chemical structure?

Lines:

  1. The line between two vertices (atoms) represents the two electrons that bond two atomic nuclei by their mutual attraction to the electrons.
  2. The first or only line between two atoms is called a sigma bond, s.
  3. Sigma bonds are longitudinal waves.
  4. The second or third line between two atoms is called a pi bond or unsaturation, p.
  5. Pi bonds are transverse waves.
  6. When the second or third line is treated just like another sigma bond the are called tau bonds, the fiction of our online drawing program.

Exam question 5:  How many pi bonds or unsaturations are in a given structure?

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Anti-Bonds

  1. For every sigma bond there is a sigma anti bond because 1 + 1 makes two.
  2. For every pi bond there is a pi anti bond because 1 + 1 makes two.

 

Unsaturated Atoms

  1. A carbon that does not have a bond to four different atoms, even if it has four bonds, is called unsaturated or not full.
  2. A nitrogen that does not have a bond to three different atoms, even if it has three bonds, is called unsaturated.
  3. An oxygen that does not have a bond to two different atoms, even if it has two bonds, is called unsaturated.
  4. Atoms connected by pi bonds or unsaturations are unsaturated.
  5. The number of unsaturated atoms does not always equal two times the number of unsaturations or pi bonds.

Exam question 6:  How many unsaturated atoms are in a given structure?

 

 

 

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Thursday, April 06, 2017 13:18