{"id":17500,"date":"2020-02-28T16:02:59","date_gmt":"2020-02-28T22:02:59","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=17500"},"modified":"2025-08-27T15:15:23","modified_gmt":"2025-08-27T20:15:23","slug":"staggered-vs-eclipsed-conformations-of-ethane","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2020\/02\/28\/staggered-vs-eclipsed-conformations-of-ethane\/","title":{"rendered":"Staggered vs Eclipsed Conformations of Ethane"},"content":{"rendered":"

Staggered vs Eclipsed Conformations of Ethane, or Why Newman Projections Are Awesome<\/strong><\/p>\n

The three-dimensional shape of methane (CH4<\/sub>) is the same under all conditions, but ethane (C2<\/sub>H6<\/sub>) and higher alkanes can assume different three-dimensional shapes due to rotation along the C-C bond.<\/p>\n

In this article: introducing conformational isomers, staggered and eclipsed conformations, the Newman projection, the dihedral angle (torsion angle), and the rotational barrier to ethane (torsional strain)!<\/p>\n

\"summary<\/a><\/p>\n

Table of Contents<\/strong><\/p>\n

    \n
  1. Recap: The Tetrahedral Structure of Methane (CH<\/span>4<\/sub><\/span>)<\/span><\/span><\/a><\/li>\n
  2. The Three-Dimensional Structure of Ethane (C2<\/sub><\/span>H<\/span>6<\/sub><\/span>)<\/span><\/span><\/a><\/li>\n
  3. Rotations Along Carbon-Carbon Bonds: Conformational Isomers Of Ethane<\/a><\/li>\n
  4. Eclipsed And Staggered Conformations Of Ethane<\/a><\/li>\n
  5. The Newman Projection of Ethane<\/a><\/li>\n
  6. The Dihedral Angle, Or Torsion Angle<\/a><\/li>\n
  7. Mapping Out The Conformations Of Ethane By Dihedral Angle<\/a><\/li>\n
  8. Torsional Strain<\/a><\/li>\n
  9. Notes<\/a><\/li>\n
  10. Quiz Yourself!<\/a><\/li>\n
  11. (Advanced) References and Further Reading<\/a><\/li>\n<\/ol>\n
    \n

    <\/a>1. Recap: The Tetrahedral Structure of Methane (CH4<\/sub>)<\/h2>\n

    In a previous post we discussed how we know that methane CH4<\/sub> is tetrahedral (See<\/em>: How Do We Know That Methane Is Tetrahedral<\/a><\/em><\/span>), as this shape maximizes the distance between the repulsive bonding electron pairs.<\/p>\n

    We also saw that CH4<\/sub> is a perfect tetrahedron, with H-C-H bond angles of 109.5 \u00b0.<\/p>\n

    To depict methane in three dimensions, it’s customary to draw two of the C\u2013H bonds with full lines to depict the C\u2013H bonds in the plane of the page. The C\u2013H bond pointing out<\/strong> of the page is drawn with a “wedge<\/strong>” (heavy) bond, and the C\u2013H bond pointing into <\/strong>(behind)\u00a0the page is drawn with a “dashed<\/strong>” bond.<\/p>\n

    This convention borrows an old artists’ trick: to give the illusion of perspective,\u00a0 depict objects in the foreground with high-contrast (heavy lines), and objects in the background with low contrast (faint lines).
    \n     Hover here for a pop-up image <\/a>.<\/p>\n

    Here’s are two “line-wedge” drawings of CH4<\/sub>. Both of these drawings depict the same three dimensional object.<\/p>\n

    \"three<\/a><\/p>\n

    Does it matter whether the “wedged” bond is drawn below or above the “dashed” bond?<\/p>\n

    No. Whether or not the wedge is drawn below or above the dash is just a matter of perspective, depicting what you’d see if you were looking “down on” or “up to” the CH4<\/sub> molecule.<\/p>\n