Context : Superclusters with collapsing cores represent dynamically evolving environments for galaxies , galaxy groups , and clusters .

Aims : We study the dynamical state and properties of galaxies and groups in the supercluster SCl A2142 that has a collapsing core , to understand its possible formation and evolution .

Methods : We find the substructure of galaxy groups using normal mixture modelling .
We have used the projected phase space ( PPS ) diagram , spherical collapse model , clustercentric distances , and magnitude gap between the brightest galaxies in groups to study the dynamical state of groups and to analyse group and galaxy properties .
We compared the alignments of groups and their brightest galaxies with the supercluster axis .

Results : The supercluster core has a radius of about 8 h ^ { -1 } Mpc and total mass M _ { \mathrm { tot } } \approx 2.3 \times~ { } 10 ^ { 15 } h ^ { -1 } M _ { \odot } and is collapsing .
Galaxies in groups on the supercluster axis have older stellar populations than off-axis groups , with median stellar ages 4 - 6 and < 4 Gyr , correspondingly .
The cluster A2142 and the group Gr8 both host galaxies with the oldest stellar populations among groups in SCl A2142 having the median stellar age t > 8 Gyr .
Recently quenched galaxies and active galactic nuclei ( AGNs ) are mostly located at virial radii or in merging regions of groups , and at clustercentric distances D _ { c } \approx 6 h ^ { -1 } Mpc .
The most elongated groups lie along the supercluster axis and are aligned with it .
Magnitude gaps between the brightest galaxies of groups are less than one magnitude , suggesting that groups in SCl A2142 are dynamically young .

Conclusions : The collapsing core of the supercluster , infall of galaxies and groups , and possible merging groups , which affect galaxy properties and may trigger the activity of AGNs , show how the whole supercluster is evolving .