Two HII region surveys are considered. The first is a multi-band survey of over one hundred hypercompact HII (HCHII) candidates using the Jansky-VLA. The second survey, the deep-resolution ALMA Three-millimetre Observations of Massive Star-forming regions (ATOMS-ALMA), studied just under 500 and identified 89 cores that cocoon HCHII or UCHII sources observed in H40α; 32 hot molecular cores (HMCs) showing more than 20 COMs; and 58 HMC candidates not associated with HII regions. The study shows how, in the vicinity of newly formed OB protostars and HII regions at an early stage of evolution, we can begin to understand the dynamics of infall, outflow, and rotational motions, as well as the feedback roles of outflows, stellar winds, and HII regions.

Through the emission observations of molecular species in the IRAS2 and IRAS4 locations in NGC 1333 in the Perseus Molecular Cloud (PMC), the distinctions between conditions favouring COMs or WCCC production in the immediate neighbourhoods of low-mass protostars are discussed. The current chemical modelling and that which will follow from accumulating higher-resolution observations using the latest generation of millimetre and submillimetre instrumentation are discussed.

Within the Large Magellanic Cloud, a hot core is observed associated with the embedded high-mass YSO (IRAS 05195˗6911), known as ST16. Comparative observations with molecular abundances typical of Galactic hot cores are discussed, as is the evidence for a rotating protostellar envelope and outflow cavity. A second LMC source, the prominent star-formation region N113, shows centrally focused star formation with associated point-like mid-infrared emission, masers, and compact HII regions superimposed on extended emission. Gas and dust appear compressed by a complex structure of ionized gas bubbles (prominent in Hα detections) engendered by massive stars in several young clusters. In both ST16 and N113 low-metallicity sources, warm dust appears to inhibit COMs formation and survival, while reaction routes appear broadly comparable with Galactic models.

The low-mass star formation Lupus complex sits within the expanding HII shell of the Upper Scorpius OB cluster, with shock impacts triggering multiple star formation. IRAS 15398 in Lupus I-1 is considered as a WCCC source rich in COMs, molecular line emissions allowing distinctions between molecules particularly prevalent in either compact or extended regions. Molecular emissions from close to the protostar as well as from gas spreading in outflow material are involved. Within the latter are found distinguishable localized components (‘blobs’) that show likely shock enhanced chemistry. As is the case for IRAS 16293 and NGC 1333, disk emission is separable from envelope emission through characteristic species and levels of molecular excitation.

Sagittarius (Sgr) B2 is the most massive star-forming region in the Galaxy and the canonical HMSFR with probably the richest source of molecules detected to date, not least in the number of COMs recorded. The consequences of a variable and higher-than-standard cosmic ionization rates in this region close to the Galactic centre are discussed. They are seen to have a complex effect on COMs chemistries, offering both an unusual test bed for chemical evolution theory, while not being conditions representative of more widely observed HMSF cores. The particular case of cyanides and isocyanides stands out, and modelling that uses enhanced but extinction-dependent CR ionization rate brings best agreement between model results and observations. Nonetheless, the modelled column densities of some species are much lower than observed, and the physical structure profile of the regions appears to be responsible.

The massive giant molecular cloud (GMC) complex Westerhout 43 (W43) and its subcores are considered, in particular G29.96. HMSF is evident in clusters and the impact of disk winds and outflows on the observable chemistry made clear. Modelling of the hot core COMs abundances matches observations for many key species observed in both this and other Galactic sources. The interaction between an HII region and an associated hot dense core is exemplified in G29.96, in spite of the evident complexity of physical conditions in the surrounding region. As in all studies made through the lens of molecular emission, astronomers are able to probe the physical conditions through trace chemical emissions.

The chapter presents two surveys of low-mass star formation regions (LMSFR). The first survey uses the IRAM (Institute for Radio Astronomy in the Millimeter Range) 30 metre telescope at Pico Veleta in Spain to identify 16 deeply embedded YSOs and the emission from eight complex organic molecules (COMs). The second survey uses ALMA (Atacama Large Millimetre Array) directed towards five low-mass candidates (all in the Serpens cluster at distances ~440 pc) and detected emission from five COMs species.