tikz.dev / chemfig Manual

chemfig

Operation of chemfig

9 Connecting bonds

By default, the lines representing single bonds do not connect, which can be too visible and unsightly when the line widths are large.

For those who find this "ugly1", it is now possible connect the single bonds with a slightly increased compilation time. The boolean ⟨key⟩ bond join = ⟨boolean⟩ macro enables this feature when ⟨true⟩ and disables it when ⟨false⟩, which is the better behavior, set by default.

Compiled output

Connecting bonds
\setchemfig{bond style={line width=3pt}}
\chemfig{-[1]-[7]} et
\chemfig[bond join=true]{-[1]-[7]}

The problem is even more obvious with Cram bonds when they connect to a single bond or another Cram bond. Here again, setting bond join to ⟨true⟩ makes for more aesthetically pleasing connections.

Compiled output

Connecting Cram bonds
\chemfig{<[:-20]>[:50]}\qquad
\chemfig[bond join]{<[:-20]>[:50]}
\medbreak
\setchemfig{cram width=5pt}
\chemfig{<[:-45]-[:30,,,,line width=5pt]>[:-10]}\qquad
\chemfig[bond join]{<[:-45]-[:30,,,,line width=5pt]>[:-10]}

It is important to note the tow following points:

  • bond join is ⟨true⟩, the Cram bond is drawn without an outline: it will therefore appear slightly thinner (the importance depending on the ⟨line width⟩ parameter);

  • bond join has no effect between a simple bond and a Cram bond when the 2 vertices of the base of the triangle of the Cram bond are outside the space delimited by the 2 parallel edges of the simple bond. Mathematically, it is the case when \(d \cos\alpha>w\), where \(d\) is the value of ⟨cram width⟩, \(w\) is the width of the single bond and \(\alpha\) is the angle between the 2 bonds.

Compiled output

Connecting Cram bonds
\setchemfig{cram width=5pt, bond join}
\chemfig{-[,,,,line width=3pt]>[:30]}\qquad
\chemfig{-[,,,,line width=3pt]>[:65]}

1 See http://tex.stackexchange.com/questions/161796/ugly-bond-joints-in-chemfig detokenize