chemtool - chemical structures editor
chemtool is a program for drawing organic molecules and exporting them as
a X bitmap, PNG, PicTeX, Xfig, SVG, SXD, MDL or EPS file. It runs under the X
Window System using the GTK widget set.
The program offers essentially unlimited undo/redo, two text fonts
plus symbols, seven colors, drawing at several zoom scales, and square and
hexagonal backdrop grids for easier alignment.
In all drawing and editing modes, mouse button one (usually the left button) is
used to mark or draw objects, while button three (the right button) can be
used to delete objects of the current type. The middle button is mainly used
in the bond drawing modes where it allows fast changing of bondtypes. Starting
with version 1.5, the default storage directory for datafiles, and the
filename extension to use, can be saved via a configuration dialog.
Bonds can be drawn in 4 different angle settings (hexagon with 30°
intervals, two pentagons with 72° intervals (different orientation),
and a 45° i octagon). (Intermediate angles are possible in all of these
modes as well - just ignore the marker points in this case).
The bond style chooser in the center of the button bar determines
the type of bond that is drawn - initially, this is a single bond. If you
want to change the type of a bond later, either click on it with the middle
button of your mouse to advance to the next type(s), or select the
appropriate type in the chooser and then switch to bondtype mode and pick
all bonds that you want to change over to the new type. (The color used for
the bond is updated at the same time if necessary.) Pressing the middle
mousebutton on a bond when in 'Bondtype' mode reverses the direction of that
Using the third (usually the right) mouse button deletes the bond
next to the cursor position.
The available bond types are:
Rings of 3 to 12 members can be drawn easily by holding down the Ctrl key while
drawing a line. This line will then become the first segment of a ring that is
automatically drawn in clockwise direction. The size of the ring defaults to
that appropriate for the selected drawing mode (i.e. 5, 6 or 8 sides), but it
can be set on a per-ring basis by pressing Ctlr-<number> before drawing
the ring, where numbers 3-9 correspond to 3 to 9-membered rings, while 0 to 2
select 10, 11 and 12-membered rings, respectively.
- single bond
- double bond
- double bond (shorter line on the other side)
- centered double bond
- triple bond (flanking lines shorter than central)
- triple bond (with equal line lengths)
- quadruple bond
- wedge-shaped bond
- dashed wedge-shaped bond
- wavy line
- half arrow
- regular arrow
- wide bond
- dotted line
- overlapping single bond (which cuts out a segment from any bond it
- light pi orbital lobe
- dark pi orbital lobe
Newly drawn rings can be deleted by pressing Ctrl and mouse button
Curved lines for objects like arrows or orbital lobes can be drawn in spline
curve mode by specifying four control points that form a bounding polygon
(startpoint, two points on either side of the peak, endpoint). Of the regular
bondtypes available in the Style menu, the 'single line', 'semiarrow', arrow
and 'dashed line' retain their usual function, while the 'wide line' type is
used to denote a filled polygon. The control points are only visible in
Move mode, where they can be dragged around to change the form of a
curve after it is drawn.
In bond style mode, clicking on any bond in the diagram changes its
representation to the type selected in the pull-down menu next to the
The additional bond type available in the pulldown menu,
is only available for drawing. It is actually a shortcut for one
of the curve drawing functions described above, with the second and third
control points automatically generated. As such, it can not be converted to
or from any of the conventional bond types.
(One can, however, convert it to any of the other curve types,
e.g. to change the type of arrowhead). The shape of the arrow will usually
need to be adjusted by shifting the control point that appears alongside it
in 'Move' mode.
Text written into the text box can be positioned with the cursor and may appear
left, middle or right-aligned in the drawing. Text size and color is
selectable from a fixed list of choices. There are two special characters to
be used for sub- and superscripting the following character:
'^' to shift up (e.g. N^+)
'_' to shift down (e.g. CH_3)
The control character '|' is used to italicise the following
character, as in |t-Bu.
A bold fonttype, typically used for numbering compounds, can be
selected by preceding the character with a '#'.
The special character '@' switches to symbol mode, which uses the
standard X11 symbol font. All alphabetic keys produce the corresponding
Greek characters in this mode, and several other symbols are available if
their standard Latin1 equivalents are already mapped onto the keyboard:
yen -> infinity
hyphen -> uparrow
macron -> downarrow
The symbols 'plusminus' and 'registered' (trademark) are already
in the standard font, although they are not normally available on the
keyboard. Use the following commands (or add the declarations to your
.xmodmaprc ) to make them available via <AltGr>+<Key>
xmodmap -e 'keysym r = r R registered' \
-e 'keysym o = o O yen' \
-e 'keysym p = p P plusminus' \
-e 'keysym u = u U hyphen' \
-e 'keysym d = d D macron'
(this leads to AltGr-P = plusminus, AltGr-R = registered in normal
mode and AltGr-O = infinity, AltGr-U = uparrow, AltGr-D = downarrow in
For 'dots-and-crosses' diagrams, the following mappings to the
symbol font might be useful: acute -> cross (e.g. keysym x = x X acute)
middle dot -> filled dot (e.g. keysym d = d D periodcentered) (using the
degree sign for the open dot).
Circled versions of the plus and minus signs for denoting ionic
charge are available as @+ and @- .
When you want to use symbols as sub- or superscripts, place the
sub- or superscripting character before the '@' character, e.g. K_@a .
In text mode, the right mouse button deletes the label at the
cursor position. Changing the size, font or color of a label can be done by
left-clicking on it after choosing the desired combination of settings. When
the text entry box above the drawing area is empty, only the settings are
updated without changing the contents of the label, otherwise the label text
is replaced as well. If you want to copy the text of an existing label to
the text entry box, click on it with the middle mouse button.
In all bond drawing modes, several keyboard shortcuts are available to add atom
symbols without having to leave drawing mode. The label is placed at the
current drawing position (the endpoint of the last line drawn, or the spot
last clicked on).
The keys 'c','h','n','o','s','p' and 'r' insert the corresponding
capital letter, 'l' (lowercase L) inserts 'Cl', while '1', '2', '3' insert
CH,CH_2 and CH_3, respectively. The asterisk key (*) inserts a filled
Pressing the space bar once allows you to enter arbitrary labels,
which will be placed at the current position when you press the Return
The keys of the numeric keypad can be used to draw short 'electron pair' lines
next to an element symbol - if one imagines the element symbol to be sitting
on the central '5' key, each key draws the appropriate electron pair for its
position. When used together with the Shift key, two dots are drawn instead of
a line - simply delete one of the dots again if you need an odd number of
For quick numbering of the atoms in a molecule, switch to one of the text modes,
hold down the Control key and pick each atom in succession with the left mouse
button. Numbering starts at 1, and the sequence can be reset at any time by
clicking the right mouse button. If you need to use your own numbering scheme,
clicking the middle button (while still holding down the Control key) makes it
pick up whatever number is in the text entry field.
If there is not enough space for your molecule you can put it in the middle of
the sheet with the center button.
You can export your molecules as an X bitmap, a PNG or EMF image, an
encapsulated postscript file, an input file for Brian Smith' xfig(1)
program, an MDL ver. 2000 molfile for data exchange with commercial packages,
an SVG file for XHTML web pages, or in the PicTeX format for direct inclusion
in LaTeX documents. The PicTeX, PNG, EMF and Postscript output functions rely
on the fig2dev81) program from the transfig(1) package and are
only available when this program was detected on startup. If the
fig2sxd(1) program is installed, an additional export option is
available for OpenOffice SXD format. Likewise, if the (open)babel program is
installed, an additional Export menu providing access to all filetypes
supported by this tool becomes available.
You can create the outputs in different sizes according to the
current zoom scale. Postscript and PicTeX files can also be created at
arbitrary scales selectable on the export file menu.
An option in the configuration menu can be set to call
fig2dev in international language mode, which will automatically
render any text written in the alternate (Times) font using the postscript
font appropriate for the current locale (currently Croatian, Cyrillic,
Czech, Hungarian, Japanese, Korean, Polish). See the fig2dev
documentation for details.
To include the PicTeX-file in your LaTeX document, you will need
the pictex macro package. Depending on the versions you use, you might also
have to load the 'color' package in the preamble of your LaTeX file. If you
experience 'TeX capacity exceeded' error messages, increase the
extra_mem_bot parameter in your texmf.cnf file (usually in
/usr/share/texmf/web2c, /usr/local/texmf or
/etc/texmf). Pictex is known for its unusual (by tex standards)
memory requirements, and the standard settings do not account for this
(although you may find a comment a la 'change this if you use pictex' in the
texmf.cnf file). Something like extra_mem_bot=400000 should not hurt
on any moderately modern system.
Since version 1.5, direct printing of diagrams to a Postscript-capable printing
device (or more typically a print queue running ghostscript) is possible. The
paper size, magnification, printer name and the print command to use
(currently either lp(1), lpr(1) or kprinter(1)) can be
stored in the Configuration Dialog.
Using the 'Mark' button, you can easily select parts of the current drawing by
enclosing them with a 'rubberband' rectangle.
If you need to add atoms outside of the rectangular area to your
selection, simply draw another rubberband around them while holding down the
The selected parts will appear highlighted in blue and are
immediately available for
To add another molecule from a previously saved chemtool drawing, select it in
the file selection window that comes up when you press the 'Add' button.
Single clicking on any filename in the list displays a small preview of the
molecule to aid in selection. The newly added molecule is automatically made
active so that it can be repositioned as desired.
- simply drag the fragment to the desired position with the mouse while
holding down the left mouse button. (If you only need to move individual
atoms or bonds, you can simply pick and drag them in 'Move' mode without
having to mark them first).
- horizontal movement of the mouse translates to smooth rotation around the
pivot point selected when pressing the mouse button
- (mirroring) the fragment about a horizontal or vertical mirror plane
through its center: this is performed by clicking on the appropriate menu
- clicking on the 'Copy' menu button creates an exact copy of the selected
fragment slightly offset to the original. The mark is automatically
transferred to the new copy.
- horizontal mouse movement is translated into a smooth increase or decrease
of size of the marked fragment
- to delete the marked fragment, simply click the third (usually the right)
mouse button after it is highlighted.
- choosing one of the icons from the drop-down list of frame and bracket
styles draws the corresponding object, e.g. a pair of round parentheses,
around the highlighted fragment.
- clicking on the 'bucket and broom' symbol invokes a function that removes
overlapping (duplicate) bonds and labels from the drawing and straightens
lines that are almost horizontal or vertical.
If you want to add it to a predefined position on another
molecule, you can mark that attachment site by left-clicking on it instead
of dragging the marker rectangle. A small green dot will appear at what is
now the reference position for the new part. If you save molecules with such
a marker set, it will in turn define their attachment site when they are
added to another drawing.
Selecting 'Templates' from the 'Tools' menu opens a second window with a small
collection of predefined structures. Simply click on the image of the desired
molecule to add it to your drawing. The Template window can be kept open
throughout a chemtool session - if it is hidden by another window, you can
move it to the front by selecting the 'Template' menu in chemtool again.
The data in the template system differ from normal chemtool
drawings only by the fact that they are stored within the program, and in a
slightly awkward format (x and y coordinates listed separately in the source
file templates.h). These are meant to provide a convenient basis set
available to all users, but not individually extendable (you can use the
'Add' function for your own structures). Please let us know if you want
specific molecules added to the templates - their name or ideally a regular
chemtool drawing file is all we need. (send email to
Chemtool provides functions for importing files in both the PDB format used by
the Protein Database (and by most molecular modeling packages) and the
proprietary MDL molfile format used by ISISdraw and understood by other
structure drawing packages and database frontends.
As both are 3D file formats, while chemtool only handles 2D
projections, imported molecules are read into a temporary storage at first
and displayed in blue on the canvas. This 3D representation can then be
rotated using the mouse. Only after pressing the Return key on the keyboard
is it converted into the final 2D projection that can be edited. While such
a 3d import is in progress, all normal drawing and editing functions are
With MDL molfile import, the carbon atom labels are automatically
discarded. For PDB import, the amount of labeling can be chosen in the file
selection dialog, which offers retention of either all labels, only those of
non-hydrogen atoms, or only the non-numeric part of the labels.
If the program babel is installed - either the original version
written by Pat Walters or the more recent OpenBabel effort - chemtool will
automatically offer a menu option for importing from any of the file formats
The distribution contains a helper program, cht(1), by Radek Liboska
(Prague) to calculate sum formula and (exact) molecular weight from a chemtool
drawing file. It is also available from within chemtool to calculate these
data for the current structure or a marked fragment of it. cht can be
misled by duplicate bonds ( chemtool does not remove overlapping bonds, such
as they might result from fusing ring systems, automatically) and by the
'aromatic ring' symbol, so you should avoid these and check the plausibility
of the generated sum formula where possible.
For features not currently supported by chemtool, like general line-drawing
functions, getting Brian Smith's XFig drawing package xfig is highly
recommended. About the only thing it does not offer is support for 'chemical'
linetypes and drawing angles - which is why chemtool was written as a sort of
companion program. (There will probably be more of the most sorely needed
drawing options added to chemtool over time, but duplicating the more
general-purpose features of xfig seems rather pointless.)
chemtool and its companion program cht are available under the
terms of the GNU General Public License (see the file 'COPYING' in the
package). This software comes with ABSOLUTELY NO WARRANTY.
- Thomas Volk
- Original author and maintainer up to 1.1.1.
- Dr. Martin Kroeker <firstname.lastname@example.org>
- Maintainer and primary author since 1.1.2.
Radek Liboska, PhD <email@example.com>
Michael Banck <firstname.lastname@example.org>
and many others.
babel(1), cht(1), fig2dev(1), fig2sxd(1),
Visit the GSP FreeBSD Man Page Interface.
Output converted with ManDoc.