Editing Structural formula (section)

== Perspective drawings ==
=== Newman projection and sawhorse projection ===

The [[Newman projection]] and the [[sawhorse]] projection are used to depict specific [[conformers]] or to distinguish [[Vicinal (chemistry)|vicinal]] stereochemistry. In both cases, two specific carbon atoms and their connecting bond are the center of attention. The only difference is a slightly different perspective: the Newman projection looking straight down the bond of interest, the sawhorse projection looking at the same bond but from a somewhat [[Oblique projection|oblique]] vantage point. In the Newman projection, a circle is used to represent a plane perpendicular to the bond, distinguishing the substituents on the front carbon from the substituents on the back carbon. In the sawhorse projection, the front carbon is usually on the left and is always slightly lower. Sometimes, an arrow is used to indicate the front carbon. The sawhorse projection is very similar to a skeletal formula, and it can even use wedges instead of lines to indicate the stereochemistry of the molecule. The sawhorse projection is set apart from the skeletal formulas because the sawhorse projection is not a very good indicator of molecule geometry and molecular arrangement. Both a Newman and Sawhorse Projection can be used to create a Fischer Projection.{{cn|date=January 2025}}

<gallery>
Image:Newman projection butane -sc.svg|Newman projection of [[butane]]
Image:Sawhorse projection butane -sc.svg|Sawhorse projection of butane
</gallery>

=== Cyclohexane conformations ===

Certain conformations of [[cyclohexane]] and other small-ring compounds can be shown using a standard convention. For example, the standard  [[Cyclohexane conformation#Chair conformation|chair conformation]] of cyclohexane involves a perspective view from slightly above the average plane of the carbon atoms and indicates clearly which groups are [[Cyclohexane conformation#Chair conformation|axial]] (pointing vertically up or down) and which are [[Cyclohexane conformation#Chair conformation|equatorial]] (almost horizontal, slightly slanted up or down). Bonds in front may or may not be highlighted with stronger lines or wedges. The conformations progress as follows: chair to half-chair to twist-boat to boat to twist-boat to half-chair to chair. The cyclohexane conformations may also be used to show the potential energy present at each stage as shown in the diagram. The chair conformations (A) have the lowest energy, whereas the half-chair conformations (D) have the highest energy. There is a peak/local maximum at the boat conformation (C), and there are valleys/local minimums at the twist-boat conformations (B). In addition, cyclohexane conformations can be used to indicate if the molecule has any 1,3 diaxial-interactions which are steric interactions between axial substituents on the 1,3, and 5 carbons.<ref name=":02">{{Cite book |last=Brown |first=William Henry |url=https://www.worldcat.org/oclc/974377227 |title=Organic chemistry |date=2018 |others=Brent L. Iverson, Eric V. Anslyn, Christopher S. Foote |isbn=978-1-305-58035-0 |edition=Eighth |location=Boston, MA |oclc=974377227}}</ref>[[File:Beta-D-Glucose.svg|thumb|Chair conformation of beta-D-Glucose|left|341x341px]]
[[File:Cyclohexane ring flip and relative conformation energies.svg|none|thumb|243x243px|The cyclohexane conformations in relation to the potential energy at each conformation]]

=== Haworth projection ===

The [[Haworth projection]] is used for cyclic [[sugar]]s. Axial and equatorial positions are not distinguished; instead, substituents are positioned directly above or below the ring atom to which they are connected.  Hydrogen substituents are typically omitted.

However, an important thing to keep in mind while reading an Haworth projection is that the ring structures are not flat. Therefore, Haworth does not provide 3-D shape. [[Norman Haworth|Sir Norman Haworth]], was a British Chemist, who won a Nobel Prize for his work on Carbohydrates and discovering the structure of Vitamin C. During his discovery, he also deducted different structural formulas which are now referred to as Haworth Projections. In a Haworth Projection a pyranose sugar is depicted as a hexagon and a furanose sugar is depicted as a pentagon. Usually an oxygen is placed at the upper right corner in pyranose and in the upper center in a furanose sugar. The thinner bonds at the top of the ring refer to the bonds as being farther away and the thicker bonds at the bottom of the ring refer to the end of the ring that is closer to the viewer.<ref name="Zhang 799">{{Cite journal |last1=Zhang |first1=Qing-zhi |last2=Zhang |first2=Shen-song |date=June 1999 |title=A New Method To Convert the Fischer Projection of a Monosaccharide to the Haworth Projection |url=https://pubs.acs.org/doi/abs/10.1021/ed076p799 |journal=Journal of Chemical Education |language=en |volume=76 |issue=6 |pages=799 |doi=10.1021/ed076p799 |issn=0021-9584|url-access=subscription }}</ref>[[File:Glucopyranose.jpg|none|thumb|[[Fischer projection|Fischer]] and [[Haworth projection|Haworth]] projection of Glucopyranose|295x295px]]
<gallery>Image:beta-D-glucose Haworth formula.svg|Haworth projection of beta-D-Glucose</gallery>

=== Fischer projection ===

The [[Fischer projection]] is mostly used for linear [[monosaccharides]]. At any given carbon center, vertical bond lines are equivalent to stereochemical hashed markings, directed away from the observer, while horizontal lines are equivalent to wedges, pointing toward the observer. The projection is unrealistic, as a saccharide would never adopt this multiply [[eclipsed]] conformation. Nonetheless, the Fischer projection is a simple way of depicting multiple sequential stereocenters that does not require or imply any knowledge of actual conformation. A Fischer projection will restrict a 3-D molecule to 2-D, and therefore, there are limitations to changing the configuration of the chiral centers. Fischer projections are used to determine the R and S configuration on a chiral carbon and it is done using the [[Cahn–Ingold–Prelog priority rules|Cahn Ingold Prelog rules]]. It is a convenient way to represent and distinguish between [[enantiomer]]s and [[diastereomer]]s.<ref name="Zhang 799" />
<gallery>
Image:DGlucose Fischer.svg|[[Glucose|Fischer projection of <small>D</small>-Glucose]]
</gallery>